Measuring Instruments and Scales is part of Physics. Below are notes on 14 sub-topics, followed by practice MCQs from State PSC and UPSC papers.

Barometer and Manometer for pressure measurement

Barometer: Instrument used to measure 1. atmospheric pressure. Barometer Reading & Weather Conditions: 2.

    • Sudden fall: Indicates stormy weather.
    • Gradual fall: Indicates rain.
    • Gradual rise: Indicates fine weather.
    • Sudden rise: Indicates cold and dry weather. Barometer in an Elevator: 3.
    • Moving upwards with increasing speed (accelerating upwards): Barometer reading increases (> normal).
    • Moving downwards with increasing speed (accelerating downwards): Barometer reading decreases (< normal).
    • At rest or constant velocity: Barometer reading remains normal. Manometer: Instrument used to measure the 4. pressure of gases. U-Tube Manometer: Primarily used for 5. measuring moderate pressures. Bourdon Pressure Gauge: Used for measur6. ing high pressures (e.g., 10⁵ Psi). Piezometer Tube: Measures gauge pressure 7. (pressure relative to atmospheric pressure). Altimeter: A type of barometer used in 8. aircraft to measure altitude. Fathometer: Measures the depth of the 9. ocean. Anemometer: Measures the velocity of wind. 10. Hygrometer: Measures humidity levels. 11. Galvanometer: Measures electric currents. 12. Tonometer: Measures the internal pressure of 13. the eye. Sphygmomanometer: Used by physicians to 14. measure blood pressure. Orificemeter: A device for measuring flow/ 15. discharge rate, generally considered the cheapest option. Mc Cleod Gauge / Pirani Gauge: Used for 16. measuring very low pressures (vacuum).

Fundamental concepts of measurement: accuracy, precision, and errors (systematic, random, gross)

  • Cathode Ray Oscilloscope (CRO): Measures voltage, frequency, and phase of electrical signals.
  • Doppler Effect: Principle used for precise tracking of moving objects (e.g., artificial satellites) by analyzing frequency shifts in emitted or reflected waves.
  • Radar (Radio Detection And Ranging): Uses radio waves to detect range, altitude, direction, and speed of objects; often incorporates the Doppler principle for speed measurement.
  • Sonar (Sound Navigation And Ranging): Uses sound waves for navigation and detection, primarily underwater.
  • Pulsar: A highly magnetized, rotating neutron star that emits beams of electromagnetic radiation; not used for artificial satellite tracking from Earth.
  • Gyroscope: Measures angular velocity and detects changes in orientation; used in navigation, stabilization, and for smartphone display rotation.
  • Accelerometer: Measures linear acceleration; detects tilt (due to gravity), free fall, shock, and vibration; used in airbag deployment and laptop hard drive protection.
  • Odometer: Measures the total distance travelled by a vehicle.
  • Speedometer: Measures the instantaneous speed of a vehicle.
  • Cathetometer: Measures vertical distances or heights without contact.
  • Lactometer: Measures the specific gravity of milk to check its purity.
  • Dilatometer: Measures dimensional changes in materials, typically due to temperature variations (thermal expansion/contraction).
  • Stethoscope: Used to auscultate (listen to) internal sounds of the body, such as heart and lung sounds.
  • Sphygmomanometer: Used to measure blood pressure.
  • Caratometer: Used to measure the purity of gold (caratage).
  • Lux Meter: Measures illuminance (intensity of light) in lux.

Galvanometer: principle, sensitivity, and conversion to Ammeter and Voltmeter

  • Galvanometer:
    • An electromechanical measuring instrument used to detect the presence and direction of small electric currents (typically microamperes to milliamperes) in a circuit.
    • Principle: Based on the magnetic effect of electric current. A currentcarrying coil, placed in a magnetic field, experiences a torque which causes deflection proportional to the current.
    • Can measure current and indicate its direction.
    • Has a low internal resistance.
  • Sensitivity of a Galvanometer:
    • Indicates the galvanometer's ability to produce a large deflection for a small current or voltage.
    • Quantitatively, it is related to the Torque/weight ratio of its moving system.
    • Current Sensitivity (Is): Deflection produced per unit current (θ/I).
    • Voltage Sensitivity (Vs): Deflection produced per unit voltage (θ/V).
  • Ammeter:
    • A device specifically designed to measure the magnitude of electric current in amperes.
    • Conversion from Galvanometer to Ammeter: A galvanometer is converted into an ammeter by connecting a very low resistance (shunt resistance, Rsh) in parallel with its coil.
      • The shunt allows most of the current to bypass the galvanometer, protecting it and extending its measurement range.
    • Ideal Ammeter: Has zero internal resistance.
    • Connection: Always connected in series with the circuit component through which current is to be measured.
    • Types: Moving coil ammeters typically measure DC current (average value), while moving iron ammeters measure AC or DC current (RMS value for AC).
  • Voltmeter:
    • A device used to measure the potential difference (voltage) between two points in an electric circuit.
    • Conversion from Galvanometer to Voltmeter: A galvanometer is converted into a voltmeter by connecting a very high resistance (Rs) in series with its coil.
      • The high series resistance limits the current drawn from the circuit and allows the galvanometer to measure a large potential difference.
    • Ideal Voltmeter: Has infinite internal resistance.
    • Connection: Always connected in parallel across the two points where the potential difference is to be measured.
  • Related Instruments/Concepts:
    • Potentiometer: Used to measure electromotive force (EMF) accurately.
    • Voltameter: An electrolytic cell used for chemical measurements, not for measuring voltage.
    • Magnetic Needle: Used to detect the presence of a magnetic field.

Hydrometer and densitometers for liquid density measurement

  • Hydrometer: Instrument used to measure the specific gravity or relative density of liquids. Operates on Archimedes' principle of buoyancy.
  • Lactometer: A type of hydrometer specifically designed to test the purity of milk by measuring its specific gravity.
  • Hygrometer: Instrument used to measure the moisture content or humidity of the atmosphere/air.
  • Pycnometer (or Density Bottle): Used for precise measurement of the density or specific gravity of liquids and sometimes powders.
  • Hypsometer: Instrument used to measure altitude by observing the boiling point of a liquid, or to measure the boiling point itself.
  • Hydrophone: An underwater device used to detect and record ocean sounds from all directions.
  • Megaphone: A horn-shaped instrument used to amplify and direct a person's voice or other sounds over a distance.
  • Anemometer: Instrument used to measure wind speed.
  • Tachometer: Instrument used to measure the rotation speed (RPM - Revolutions Per Minute) of a shaft or disk, e.g., in engines.

Least count and significant figures in measurements

  • Least Count (LC): Smallest value an instrument can measure.
  • Precision: A measurement's precision is directly related to the instrument's least count; smaller LC means higher precision.
  • LC for Vernier Caliper: Smallest main scale division / Total number of divisions on vernier scale.
  • LC for Screw Gauge: Pitch / Total number of divisions on circular scale.
  • Pitch of Screw Gauge: Distance moved by screw / Number of rotations.
  • Significant Figures (SF): Digits in a measurement considered reliable and contributing to its precision.
  • SF Rule 1 (Non-zero digits): All non-zero digits are significant (e.g., 234.5 has 4 SF).
  • SF Rule 2 (Sandwich zeros): Zeros between non-zero digits are significant (e.g., 1005 has 4 SF).
  • SF Rule 3 (Leading zeros): Zeros before nonzero digits (leading zeros) are NOT significant (e.g., 0.0023 has 2 SF).
  • SF Rule 4 (Trailing zeros with decimal): Trailing zeros are significant ONLY if the number contains a decimal point (e.g., 2.00 has 3 SF; 200 has 1 SF, but 200. has 3 SF).
  • SF Rule 5 (Exact numbers): Exact counts or defined constants have infinite significant figures.
  • SF in Addition/Subtraction: Result is rounded to the same number of decimal places as the measurement with the fewest decimal places.
  • SF in Multiplication/Division: Result is rounded to the same number of significant figures as the measurement with the fewest significant figures.
  • Rounding Rule (< 5): If the digit to be dropped is less than 5, the preceding digit remains unchanged.
  • Rounding Rule (> 5): If the digit to be dropped is greater than 5, the preceding digit is increased by 1.
  • Rounding Rule (= 5): If the digit to be dropped is 5 (and there are no other digits after it or they are zeros), the preceding digit is increased by 1 if it's odd, and remains unchanged if it's even.

Liquid-in-glass thermometers: types (clinical, laboratory) and their working

  • Liquid-in-glass thermometers measure temperature based on thermal expansion/contraction of a liquid (e.g., mercury, alcohol) in a sealed glass tube.
  • Working Principle: Liquid expands when heated, rises in the capillary tube; contracts when cooled, falls in the tube. The level indicates temperature on a calibrated scale.
  • Clinical Thermometer:
    • Purpose: Measures human body temperature.
    • Liquid: Typically Mercury (historically, now less common due to safety) or Alcohol.
    • Range: Narrow, usually 35°C to 42°C (94°F to 108°F).
    • Feature: Has a 'kink' or constriction near the bulb to prevent the mercury level from falling back immediately, allowing for reading after removal from the body.
  • Laboratory Thermometer:
    • Purpose: Measures temperature in laboratory experiments.
    • Liquid: Mercury or Alcohol.
    • Range: Wider, typically -10°C to 110°C.
    • Feature: No kink/constriction; the liquid level falls immediately upon removal from the heat source.
  • Temperature Scales & Conversions:
    • Celsius (°C), Fahrenheit (°F), Kelvin (K).
    • Conversion Formulas:
      • °F = (°C × 9/5) + 32
      • °C = (°F - 32) × 5/9
      • K = °C + 273.15 (approx. 273 for exam purposes).
    • Key Equivalences:
      • 0°C = 32°F = 273.15 K (Freezing point of water).
      • 100°C = 212°F = 373.15 K (Boiling point of water).
      • -40°C = -40°F (The only point where Celsius and Fahrenheit scales read the same value).
    • Example: 40°C = (40 × 9/5) + 32 = 72 + 32 = 104°F.
    • Example: 273 K ≈ 0°C = (0 × 9/5) + 32 = 32°F.
  • Other Measuring Instruments:
    • Hypsometer: Measures the boiling point of liquids (and can infer altitude).
    • Stethoscope: Used for hearing heartbeats and other internal body sounds.
    • Sphygmomanometer: Used for measuring blood pressure.
    • Lux meter: Used for measuring the intensity of light.

Physical balance and weighing techniques

  • A physical balance (beam balance) measures mass by comparing an unknown mass with standard masses. It works on the principle of moments and is independent of acceleration due to gravity (g). Thus, it measures the true mass of an object, irrespective of location.
  • A spring balance measures weight (force) by the extension or compression of a spring. It operates based on Hooke's Law.
  • Weight (W) = mass (m) × acceleration due to gravity (g).
  • A spring balance is typically calibrated to display mass, assuming a specific standard value of 'g' at its manufacturing or calibration location.
  • The measurement of mass taken by a spring weighing balance is correct (accurate) only at places where the acceleration due to gravity (g) is the same as the place where the spring balance was calibrated for.
  • The reading of a spring balance will vary with changes in 'g' (e.g., different at poles vs. equator, at different altitudes, or on different celestial bodies), meaning its displayed mass reading would be incorrect if 'g' differs from the calibration 'g'.

Potentiometer: principle, construction, and applications (e.g., measuring EMF, internal resistance)

  • Principle: Measures potential difference (PD) or electromotive force (EMF) accurately without drawing current from the source.
  • Working Principle: Based on the null deflection method. When a constant current flows through a wire of uniform cross-section and composition, the potential drop across any portion of the wire is directly proportional to its length (V ∝ L).
  • Construction: Consists of a long uniform resistance wire (typically 4-10m, made of manganin or constantan due to high resistivity and low-temperature coefficient of resistance), a driver cell (auxiliary battery), a rheostat (to adjust current), a galvanometer, a jockey, and a resistance box.
  • Applications:
    • 1. Comparing EMFs of two cells (E₁ and E₂):
      • The balance length (L₁) is found for cell E₁.
      • The balance length (L₂) is found for cell E₂.
      • Ratio: E₁/E₂ = L₁/L₂.
    • 2. Measuring the Internal Resistance (r) of a cell:
      • First, find the balance length (L₁) when the cell is in an open circuit (measures EMF, E).
      • Next, connect a known resistance (R) from a resistance box in parallel with the cell, and find the new balance length (L₂) (measures terminal PD, V).
      • Formula: r = R ((L₁/L₂) - 1).
    • 3. Measuring the EMF of a cell:
      • If the potential gradient (k) of the wire is known (k = potential drop per unit length), then EMF (E) = k L (where L is the balance length).
      • Alternatively, compare with a standard cell of known EMF (as in comparing EMFs).
  • Advantage: Does not draw any current from the cell at the balance point, hence measures the true EMF.

Principles of calibration and standardization of measuring instruments

  • Calibration: Process of comparing a measuring instrument's readings against a known standard to determine accuracy and make necessary adjustments.
  • Standardization: Establishing a common basis for measurements, ensuring consistency and comparability across instruments and locations, often linked to international standards (e.g., SI units).
  • Hypsometer: Instrument primarily used for calibrating thermometers at the steam point (boiling point of water).
  • Hypsometer Principle: Determines the precise boiling point of a liquid (typically water) at a given atmospheric pressure, providing a known reference temperature for thermometer calibration.
  • Steam Point (Boiling Point of Water): A fundamental fixed point (100°C or 212°F at standard atmospheric pressure) used in thermometer calibration; its value varies with pressure.

Screw Gauge (Micrometer): principle, construction, reading, and applications

Principle: Operates on the principle that the 1. linear distance moved by a screw is directly proportional to its rotation. Pitch: The linear distance moved by the 2. screw for one complete rotation of the circular scale (e.g., 0.5 mm or 1 mm). Least Count (LC): The smallest length that 3. can be measured.

    • Formula: LC = Pitch / Total number of divisions on the circular scale.
    • More accurate than Vernier Callipers. Construction (Key Parts): 4.
    • U-frame: Main body.
    • Stud: Fixed end.
    • Screw: Movable jaw, attached to the thimble.
    • Pitch Scale (Main Scale): Graduated scale (mm or cm) along the axis of the screw.
    • Circular Scale: Divisions (e.g., 50 or 100) around the circumference of the thimble.
    • Ratchet Stop: Ensures uniform pressure and prevents overtightening. Reading: 5.
    • Total Reading = Main Scale Reading (MSR) + (Circular Scale Reading (CSR) × LC) - Zero Error.
    • MSR: The last visible division on the pitch scale before the edge of the thimble.
    • CSR: The division on the circular scale that coincides with the pitch line (reference line) of the main scale. Zero Error: Occurs when the screw tip 6. touches the stud without any object between them.
    • Positive Zero Error: If the zero of the circular scale is below the pitch line. Calculated as `+ (Coinciding circular scale division × LC)`.
    • Negative Zero Error: If the zero of the circular scale is above the pitch line. Calculated as `- [(Total circular divisions - Coinciding circular scale division) × LC]`.
    • Zero Correction: Is the negative of the zero error. Applications: Used for precise measurement 7. of very small lengths.
    • Thickness of thin wire.
    • Diameter of a small sphere or cylinder.
    • Thickness of a sheet (e.g., paper, glass).

Stopwatch and principles of time measurement

  • Stopwatch: Device for measuring time intervals accurately.
  • Clocks (Analog):
    • Hour Hand: Rotates 360° in 12 hours (30°/hour or 0.5°/minute).
    • Minute Hand: Rotates 360° in 60 minutes (6°/minute).
  • Faulty Clocks (Gaining/Losing Time):
    • If a clock gains X minutes in Y hours:
      • True time interval: Y hours (Y60 minutes)
      • Faulty clock interval: Y hours + X minutes ((Y60)+X minutes)
    • If a clock loses X minutes in Y hours:
      • True time interval: Y hours (Y60 minutes)
      • Faulty clock interval: Y hours X minutes ((Y60)-X minutes)
    • Calculation of True Time: `True Time = (Observed time on faulty clock) (True interval / Faulty clock interval)`
    • Calculation of Faulty Time: `Faulty Time = (Actual true time) (Faulty clock interval / True interval)`
  • Atomic Clocks:
    • Principle: Based on the precise and constant resonant frequency (microwave energy absorption/emission) associated with electron transitions within atoms.
    • Primary Standard Element: Caesium-133 atom is widely used.
    • World's Most Precise Atomic Clock (NIST, USA): Based on Aluminium (Al) atom.
  • Measuring Instruments:
    • Seismograph: Records ground motion (seismic waves) caused by earthquakes, used to determine intensity/ magnitude.
    • Speedometer: Measures the instantaneous speed of a vehicle.
    • Odometer: Measures the total distance traveled by a vehicle.

Thermocouples and their applications in temperature measurement

  • Thermocouple: A sensor measuring temperature via voltage produced by the Seebeck effect.
  • Principle (Seebeck Effect): When two dissimilar electrical conductors are joined at two points, and these junctions are maintained at different temperatures, a voltage (electromotive force, EMF) is generated in the circuit.
  • Mechanism: One junction (measuring junction) is exposed to the temperature to be measured, and the other (reference junction) is kept at a known reference temperature.
  • Output: The generated voltage is proportional to the temperature difference between the junctions.
  • Temperature Range: Capable of measuring a wide range of temperatures, including high temperatures (e.g., -200°C to 2300°C depending on material type).
  • Applications: Industrial process control, scientific research, engine exhaust gas temperature, furnaces.
  • Pyrometer: An instrument specifically used for measuring very high temperatures (e.g., above 1000°C) and temperatures of distant objects.
  • Type: Pyrometers are primarily radiation thermometers.
  • Mechanism: They measure temperature by detecting the thermal radiation emitted by the hot object, without physical contact.
  • Advantage: Ideal for extremely high temperatures, moving targets, or objects in hazardous environments where contact measurement is impractical.

Vernier Calipers: principle, construction, reading, and applications

  • Principle: Works on the principle of difference between one Main Scale Division (MSD) and one Vernier Scale Division (VSD).
  • Least Count (LC): The smallest length that can be measured accurately by the instrument.
    • LC = 1 MSD - 1 VSD.
    • Alternatively, LC = (Smallest division on Main Scale) / (Total number of divisions on Vernier Scale).
    • Standard Least Count: Typically 0.1 mm or 0.01 cm.
  • Construction:
    • Main Scale: Fixed, graduated in cm and mm.
    • Vernier Scale: Movable scale that slides along the main scale.
    • Jaws: Outer jaws (for external dimensions), Inner jaws (for internal dimensions).
    • Depth Bar/Rod: Attached to the movable jaw for measuring depth.
    • Locking Screw: To fix the Vernier scale position.
    • Thumb Screw: For fine adjustment of the movable jaw.
  • Reading (Measurement):
    • Total Reading = Main Scale Reading (MSR) + (Vernier Coincidence (VC) × Least Count (LC)) - Zero Error (ZE).
    • Main Scale Reading (MSR): The reading on the main scale just before the zero mark of the Vernier scale.
    • Vernier Coincidence (VC): The division on the Vernier scale that exactly coincides with any division on the main scale.
    • Zero Error (ZE): Error when the jaws are completely closed.
      • Positive Zero Error: Vernier zero mark is to the right of the main scale zero. ZE = +(VCzero × LC).
      • Negative Zero Error: Vernier zero mark is to the left of the main scale zero. ZE = -((Total VSD - VCzero) × LC).
    • Corrected Reading = Observed Reading - Zero Error.
  • Applications: Used to measure:
    • External diameter/length of an object.
    • Internal diameter of a hollow object.
    • Depth of holes or small vessels.

Wheatstone Bridge: principle and applications in resistance measurement

  • Wheatstone Bridge (DC Bridge): An electrical circuit used to accurately measure an unknown electrical resistance by balancing two legs of a bridge circuit.
  • Principle (Null Deflection Method): The bridge is said to be balanced when the galvanometer (connected between two opposite junctions) shows zero deflection, indicating no current flows through it. At this point, the potential difference across the galvanometer is zero.
  • Components: Consists of four resistive arms (P, Q, R, S), a galvanometer, and a DC voltage source. P, Q are ratio arms; R is a known variable resistance; S is the unknown resistance.
  • Balance Condition: When the bridge is balanced, the ratio of resistances in the arms is equal: P/Q = R/S.
  • Measurement of Unknown Resistance: If P, Q, and R (standard known variable resistance) are known, the unknown resistance S can be calculated as S = R (Q/P).
  • Sensitivity: The sensitivity of a Wheatstone bridge depends on the galvanometer's sensitivity and the relative values of the arm resistances. Maximum sensitivity is achieved when all four arms have similar resistance values.
  • Applications:
    • Precise measurement of unknown electrical resistance.
    • Used in strain gauges (resistance changes with mechanical strain).
    • Used in thermistors and resistance thermometers (resistance changes with temperature).
  • Meter Bridge (Slide Wire Bridge): A practical application of the Wheatstone bridge for resistance measurement.
    • Uses a uniform resistance wire (typically 1 meter long) as two arms (P and Q).
    • The balance point is found by sliding a jockey along the wire until the galvanometer shows zero deflection.
    • The ratio of resistances P/Q is replaced by the ratio of the lengths of the wire segments (l1 and l2) on either side of the balance point.
    • Formula: R/S = l1/l2, where R is known, S is unknown, l1 and l2 are balancing lengths. Thus, S = R (l2/l1).

3. Mechanics

Practice MCQs: Measuring Instruments and Scales

Barometer and Manometer for pressure measurement

  1. Which of the following instruments is used for measuring the depth of the ocean ?

    Asked in: HPPSC HPAS Prelims 2016 · WBCS Main Paper 4 2019

    1. Galvanometer
    2. Ammeter
    3. Barometer
    4. Fathometer
    Show answer

    Answer: D. Fathometer

    A fathometer, also known as an echo sounder, is an instrument used to determine the depth of a body of water by transmitting sound waves into the water C. Cr D. Cq Ans: B Radioactivity is the process of spontaneous decay of atomic nuclei. The rate of this decay is measured in units like Becquerel (Bq), the SI unit, or Curie (Ci).

  2. Which of the following are units of the pressure ? (A) bar (B) Pa (C) torr (D) atm Choose the correct option :

    Asked in: ras 2025 2025

    1. Only (B) and (D)
    2. Only (B), (C) and (D)
    3. Only (A), (B) and (D)
    4. All (A), (B), (C) and (D)
    Show answer

    Answer: D. All (A), (B), (C) and (D)

    Pressure is defined as force per unit area. Various units are used to measure pressure based on historical context, scientific discipline, and practical application. and measuring the time it takes for the echo to return after bouncing off the bottom.

  3. Match the names of scientific instruments in Column I with their designated fields of applications in Column II and select the correct answer using the options given below the columns : Column I Column II 1. Galvanoa. Measure internal pressure of meter the eye 2. Hygrometer b. Measure electric currents 3. Manometer c. Measure humidity levels 4. Tonometer d. Pressure of gases

    Asked in: HAS Prelims 2019

    1. 1-d, 2-a, 3-c, 4-b
    2. 1-b, 2-c, 3-d, 4-a
    3. 1-c, 2-d, 3-a, 4-c
    4. 1-a, 2-c, 3-b, 4-d
    Show answer

    Answer: B. 1-b, 2-c, 3-d, 4-a

    - A Galvanometer is used to detect and measure small electric currents. - A Hygrometer is used to measure the amount of water vapor in the air or other gases, i.e., humidity. - A Manometer is used to measure the pressure of fluids, typically gases. - A Tonometer is a medical instrument used to measure the intraocular pressure (internal pressure of the eye), commonly used to screen for glaucoma.

  4. Which one of the following devices is used to measure atmospheric pressure ?

    Asked in: UPSC NDA 1 2018

    1. Ammeter
    2. Barometer
    3. Potentiometer
    4. Lactometer
    Show answer

    Answer: B. Barometer

    Atmospheric pressure is the pressure exerted by the weight of the air column above a point on Earth's surface. Devices like mercury barometers (Torricelli's principle) or aneroid barometers are designed to measure this pressure.

  5. A Barometer kept in an elevator reads 760 mm when the elevator is at rest. When the elevator moves in the upward direction with increasing speed, the reading of the Barometer will be:

    Asked in: UPSC CAPF 2016

    1. 760 mm
    2. < 760 mm
    3. > 760 mm
    4. Zero
    Show answer

    Answer: C. > 760 mm

    This question tests the understanding of apparent weight and pressure measurement in accelerating reference frames.

  6. The velocity of wind is measured by

    Asked in: UPPCS Prelims 2016

    1. Barometer
    2. Anaemometer
    3. Hydrometer
    4. Wind Vane
    Show answer

    Answer: B. Anaemometer

    An anemometer is an instrument used for measuring wind speed. Common types include cup anemometers, propeller anemometers, and ultrasonic anemometers.

  7. Which of the following weather conditions is indicated by a sudden fall in barometer reading?

    Asked in: UPPCS Prelims 2001

    1. Stormy weather
    2. Calm weather
    3. Cold and dry weather
    4. Hot and sunny Weather
    Show answer

    Answer: A. Stormy weather

    Decreasing atmospheric pressure is typically associated with the approach of a low-pressure system. Low-pressure systems are often linked to unstable air conditions, rising air, cloud formation, precipitation, and strong winds, which collectively indicate stormy weather. A sudden or rapid fall signifies a fast-moving or intense low-pressure system.

Fundamental concepts of measurement: accuracy, precision, and errors (systematic, random, gross)

  1. A Cathode Ray Oscilloscope (CRO) is used to measure ______ of a signal.

    Asked in: TNPSC CS Prelims 2019

    1. voltage
    2. frequency
    3. phase
    4. all the above
    Show answer

    Answer: D. all the above

    - Voltage: The vertical deflection of the electron beam on the screen is directly proportional to the instantaneous input voltage, allowing measurement of peak voltage, peak-to-peak voltage, etc. - Frequency: By setting a known time base (sweep speed) on the horizontal axis, the period (time taken for one cycle) of the waveform can be measured. The frequency is the reciprocal of the period (f = 1/ T). - Phase: By simultaneously displaying two related signals or using the triggering function appropriately, the phase difference between two signals can be determined.

  2. An artificial satellite can be tracked very precisely from the earth by using

    Asked in: UPPCS Prelims 2017

    1. Doppler effect
    2. Radar
    3. Sonar
    4. Pulsar
    Show answer

    Answer: B. Radar

    Radar (Radio Detection and Ranging) systems work by transmitting radio waves and detecting the reflected signals from an object. By measuring the time delay of the reflected signal and its direction, the distance, position, and velocity of the object can be determined.

  3. Consider the following actions: 1. Detection of car crash/collision which results in the deployment of airbags almost instantaneously. 2. Detection of accidental free fall of a laptop towards the ground which results in the immediate turning off of the hard drive 3. Detection of the tilt of smartphone which results in the rotation of display between portrait and landscape mode In which of the above actions is the function of a gyroscope is used?

    Asked in: UPSC IAS 2023

    1. 1 and 2 only
    2. 2 and 3 only
    3. 1 and 3 only
    4. 1, 2 and 3
    Show answer

    Answer: D. 1, 2 and 3

    A gyroscope measures angular velocity (rate of rotation). In modern devices, gyroscopes are often used alongside accelerometers (which measure linear acceleration and tilt due to gravity) in Inertial Measurement Units (IMUs) to determine full 3D orientation and motion. 1. Car crash/collision Advanced automotive crash detection systems use IMUs containing both accelerometers and gyroscopes. While accelerometers are crucial for detecting sudden deceleration (impact), gyroscopes can provide data on the vehicle's rotation (pitch, roll, yaw) during a crash sequence, which is vital for determining the severity and type of crash (e.g., rollover) and optimizing airbag deployment strategies. Thus, the function of a gyroscope is used.

  4. Laptop accidental free fall Many modern laptops have sensors to detect free fall and suddenly stop the hard drive head to prevent damage upon impact. While accelerometers are primary in detecting the acceleration due to gravity and the subsequent impact deceleration, gyroscopes can be used in conjunction to better characterize the motion (e.g., determining if the laptop is rotating during the fall), improving the accuracy and reliability of the free fall detection system. Thus, the function of a gyroscope can be used. 3. Smartphone tilt for display rotation While the basic detection of static tilt relative to gravity is done by accelerometers, modern smartphones use gyroscopes in combination with accelerometers (IMU) for more accurate, stable, and responsive orientation sensing. The gyroscope measures angular velocity, allowing the phone to detect rotations quickly and smoothly, distinguish intentional rotations from accidental movements, and provide faster screen transitions between portrait and landscape modes. Thus, the function of a gyroscope is used. 15. Automobiles are fitted with a device that shows the distance travelled. Such a device is known as

    Asked in: UPSC CISF AC EXE 2017

    1. Speedometer
    2. Cathetometer
    3. Odometer
    4. Lactometer
    Show answer

    Answer: C. Odometer

    - An odometer is specifically designed to measure the distance covered by a vehicle. - A speedometer measures speed. - Other options are not used in automobiles for measuring distance traveled.

  5. Dilatometer is used for the measurement of

    Asked in: WBPSC CS Prelims 2021

    1. electrical energy
    2. mechanical energy
    3. dimensional change in material
    4. thermal energy
    Show answer

    Answer: C. dimensional change in material

    A dilatometer is an instrument used to measure changes in the physical dimensions of a material as a function of temperature or other physical factors like pressure. This measurement is often used to determine properties such as thermal expansion coefficient, softening point, and phase transitions.

  6. Match List–I with List–II and select the correct answer using the code given below the lists : List–I List–II 1. To measure intensity of (a) Stethoscope light (b) Sphygnomano‐ 2. To check purity of gold meter (c) Caratometer 3. To hear heart sound 4. To measure blood pres‐ (d) Lux meter sure

    Asked in: UPPCS Prelims 2008

    1. 1 2 3 4
    2. 4 3 2 1
    3. 3 4 2 1
    4. 2 1 4 3
    Show answer

    Answer: C. 3 4 2 1

    The question requires matching common scientific/ medical instruments with their primary functions. Understanding the basic use of these devices is key.

Galvanometer: principle, sensitivity, and conversion to Ammeter and Voltmeter

  1. The device to measure electric current is

    Asked in: BPSC Prelims Exam 64th

    1. voltmeter
    2. ammeter
    3. voltameter
    4. potentiometer
    Show answer

    Answer: B. ammeter

    BPSC Prelims Exam-65th An ammeter is an instrument used to measure the flow of electric current in a circuit. It is always connected in series with the component through which the current is to be measured.

  2. Which of the following is not correctly matched?

    Asked in: BPSC Prelims Exam 67th Cancelled

    1. Voltmeter—Potential difference
    2. Ammeter—Electric current
    3. Potentiometer—Electromotive force
    4. Galvanometer—Electric resistance
    Show answer

    Answer: D. Galvanometer—Electric resistance

    A galvanometer is an instrument used for detecting the presence and direction of small electric currents. While it is a crucial component in circuits designed to measure resistance (like a Wheatstone bridge where it detects null deflection), it does not directly measure electric resistance itself.

  3. The device used for measuring electric current in a circuit is called

    Asked in: UPSC CDS 2 2022

    1. Ammeter
    2. Motor
    3. Voltmeter
    4. Generator
    Show answer

    Answer: A. Ammeter

    - An ammeter is connected in series within the circuit to measure the total current flowing through that part of the circuit.

  4. Which of the following can be used to determine the polarity of an unmarked bar magnet?

    Asked in: UPSC Geoscientist 2022

    1. An electroscope
    2. Iron filings
    3. A compass
    4. Another unmarked bar magnet
    Show answer

    Answer: C. A compass

    - A compass needle has known magnetic poles. - Magnetic poles interact (like repel, opposite attract). - Using a compass, one can identify the poles of an unknown magnet by observing attraction/repulsion.

  5. Radioactivity is measured by

    Asked in: UPSC NDA 2 2017

    1. GM Counter
    2. Polarimeter
    3. Calorimeter
    4. Colorimeter
    Show answer

    Answer: A. GM Counter

    - Radioactivity involves the emission of ionizing radiation. - A GM Counter is an instrument that detects ionizing radiation.

  6. The instrument used for detecting the presence of electric current in a circuit is

    Asked in: UPSC NDA 2 2020

    1. Refractometer
    2. Galvanometer
    3. Viscometer
    4. Diffractometer
    Show answer

    Answer: B. Galvanometer

    A galvanometer is an electrical instrument used for detecting the presence of electric current in a circuit and also for measuring its direction and magnitude (although ammeters are typically used for precise magnitude measurement).

  7. The presence of magnetic field can be determined using which one of the following instruments?

    Asked in: UPSC NDA 2 2022

    1. Ammeter
    2. Voltmeter
    3. Magnetic needle
    4. Motor
    Show answer

    Answer: C. Magnetic needle

    A magnetic needle, like the one in a compass, is a small magnet pivoted to rotate freely. When placed in a magnetic field, it aligns itself with the direction of the field lines, indicating the presence and direction of the field.

Hydrometer and densitometers for liquid density measurement

  1. Match List I with List II and choose the correct answer from the given options : List I List II (a) Hy‐ (i) An instrument measuring the rodrophone tation speed of a shaft or disk (b) Mega‐ (ii) An instrument that measures phone wind speed (c) Anem‐ (iii) An instrument that spreads ometer sound to far-off places (iv) An underwater device that de‐ (d) Tatects and records ocean sounds from chometer all directions

    Asked in: HPPSC HPAS Prelims 2021

    1. (iv) (iii) (ii) (i)
    2. (i) (iii) (ii) (iv)
    3. (i) (ii) (iv) (iii)
    4. (iv) (iii) (ii) (i)
    Show answer

    Answer: A. (iv) (iii) (ii) (i)

    Hydrophone detects underwater sound, Megaphone spreads sound over distance, Anemometer measures wind speed, and Tachometer measures rotational speed.

  2. Which one of the following instruments is used for measuring moisture content of air ?

    Asked in: UPSC CAPF 2017

    1. Hydrometer
    2. Hygrometer
    3. Hypsometer
    4. Pycnometer
    Show answer

    Answer: B. Hygrometer

    - A hygrometer is an instrument used to measure the amount of water vapor in the air, soil, or confined spaces. This is commonly known as humidity. - A hydrometer is used to measure the specific gravity (or relative density) of liquids, i.e., the ratio of the density of the liquid to the density of water. - A hypsometer is used to measure elevations or the boiling point of a liquid. - A pycnometer is a device used to measure the density of solids or liquids.

  3. Relative humidity of atmosphere is measured by:

    Asked in: UPPCS Prelims 1995

    1. Hydrometer
    2. Hygrometer
    3. Potentiometer
    4. Lactometer
    Show answer

    Answer: B. Hygrometer

    Humidity is measured using a hygrometer.

Least count and significant figures in measurements

  1. The first number in common size viz 14/20, 19/22 and 24/40 for ground glass joints refers to

    Asked in: JUNIOR laboratory assistant 2025

    1. Outer diameter (in millimeter) of a female joint or inner diameter of a male joint
    2. Inner diameter (in millimeter) of a female joint or outer diameter of a male joint
    3. Length of the joint
    4. All of the above
    Show answer

    Answer: B. Inner diameter (in millimeter) of a female joint or outer diameter of a male joint

    Ground glass joints are standardized connectors used in laboratory glassware to create airtight seals between different pieces of equipment. The numbering system ensures compatibility between male and female joints of the same size.

Liquid-in-glass thermometers: types (clinical, laboratory) and their working

  1. The value of 40 degrees Celsius in Fahrenheit scale is

    Asked in: BPSC Prelims Exam 64th

    1. 104 °F
    2. 100 °F
    3. 102 °F
    4. 75 °F
    Show answer

    Answer: A. 104 °F

    The formula for converting temperature from Celsius (°C) to Fahrenheit (°F) is: °F = (°C × 9/5) + 32.

  2. The liquid used in a clinical thermometer is :

    Asked in: HPPSC HPAS Prelims 2017

    1. Alcohol
    2. Water
    3. Mercury
    4. Benzene
    Show answer

    Answer: C. Mercury

    Mercury is preferred for clinical thermometers due to its properties: it expands uniformly with temperature, remains liquid over a wide temperature range relevant to body temperature, does not stick to the glass, and is easily visible.

  3. Numerically two thermometers, one in Fahrenheit scale and another in Celsius scale shall read same at

    Asked in: UPSC NDA 1 2021

    1. – 40°
    2. 0°
    3. – 273°
    4. 100°
    Show answer

    Answer: A. – 40°

    To find the point where the two scales read the same, we set the temperature in Fahrenheit ($T_F$) equal to the temperature in Celsius ($T_C$) and use the conversion formula: $T_F = T_C$. Let this common temperature be $x$. The conversion formula from Celsius to Fahrenheit is $T_F = T_C \times \frac{9}{5} + 32$. Substituting $x$ for both $T_F$ and $T_C$: $x = x \times \frac{9}{5} + 32$. Solving for $x$: $x - \frac{9x}{5} = 32 \implies \frac{5x - 9x}{5} = 32 \implies \frac{-4x} {5} = 32 \implies -4x = 160 \implies x = \frac{160} {-4} = -40$. Thus, -40°C is equal to -40°F.

  4. Hypsometer is used to measure :

    Asked in: OPSC CS Prelims 2020

    1. The pressure of gas
    2. The boiling point of liquids
    3. The level of humidity
    4. The depth of ocean
    Show answer

    Answer: B. The boiling point of liquids

    - The boiling point of a liquid depends on the surrounding atmospheric pressure. - Atmospheric pressure decreases with increasing altitude.

  5. If a scientist reads an ambient temperature 273 K in the laboratory, what will a doctor's thermometer read it ?

    Asked in: UPSC CAPF 2014

    1. 0 degree Fahrenheit
    2. 32 degrees Fahrenheit
    3. 99 degrees Fahrenheit
    4. – 100 degrees Fahrenheit
    Show answer

    Answer: B. 32 degrees Fahrenheit

    To convert temperature from Kelvin (K) to Fahrenheit (°F), we first convert Kelvin to Celsius (°C) and then Celsius to Fahrenheit. The formula for converting Kelvin to Celsius is: °C = K - 273.15 Given temperature is 273 K. °C = 273 - 273.15 = -0.15 °C. However, in many contexts, 273 K is treated as approximately 0°C, especially in simplified problems like this. Let's use 0°C.The formula for converting Celsius to Fahrenheit is: °F = (°C × 9/5) + 32 Using °C = 0: °F = (0 × 9/5) + 32 °F = 0 + 32 °F = 32.So, 273 K is equivalent to 32°F. This corresponds to the freezing point of water.

  6. Match List–I with List–II and select the correct answer using the codes given below the Lists : List—I a. Stethoscope b. Sphygmomanometer c. Lux meter d. Thermometer List—II 1. For hearing heart beat 2. For measuring intensity of light 3. For measuring blood pressure 4. For measuring temperature Codes : (A) a b c d 1 3 2 4 (B) a b c d 1 2 3 4 (C) a b c d 3 2 1 4 (D) a b c d 1 4 2 3

    Asked in: BJS 2023

    1. a:1, b:3, c:2, d:4
    2. a:1, b:2, c:3, d:4
    3. a:3, b:2, c:1, d:4
    4. a:1, b:4, c:2, d:3
    Show answer

    Answer: A. a:1, b:3, c:2, d:4

    BJS -2023 This question tests the knowledge of common scientific instruments and their functions.

Physical balance and weighing techniques

  1. Which one of the following statements is correct ?

    Asked in: UPSC NDA 2 2016

    1. The measurement of mass taken by a spring weighing balance is correct at the place where the spring balance is calibrated for
    2. The measurement of mass taken by a spring weighing balance is correct at all places
    3. The measurement of mass taken by a spring weighing balance is correct at the places where the acceleration due to gravity is same as the place where the spring balance is calibrated for
    4. A spring balance cannot be used to measure mass at any place
    Show answer

    Answer: C. The measurement of mass taken by a spring weighing balance is correct at the places where the acceleration due to gravity is same as the place where the spring balance is calibrated for

    A spring balance is calibrated at a specific location where the local acceleration due to gravity ('g') has a particular value. The scale on the spring balance is marked to show mass based on the extension of the spring caused by the weight. If the spring balance is used at a location where the acceleration due to gravity is different from the calibration location, the weight of the same mass will be different, leading to a different spring extension and consequently an incorrect mass reading on the scale. Therefore, the measurement of mass taken by a spring balance is correct only at places where the acceleration due to gravity is the same as the place where it was calibrated.

Potentiometer: principle, construction, and applications (e.g., measuring EMF, internal resistance)

  1. Two-point problem and three-point problem are the methods of

    Asked in: Civil Engg GA 24 2023 CO 1505 2024

    1. orientation
    2. resection
    3. traversing and resection
    4. orientation and resection
    Show answer

    Answer: D. orientation and resection

    Two-point and three-point problems are fundamental techniques in plane tabling and surveying for determining the unknown position of a station (resection) and orienting the instrument or map.

Principles of calibration and standardization of measuring instruments

  1. 78.Which of the following instrument is used to calibrate thermometers at steam temp.

    Asked in: RPSC RAS Prelims 1996

    1. Thermostate
    2. Pyrometer
    3. Hypsometer
    4. Hygrometer
    Show answer

    Answer: C. Hypsometer

    A Hypsometer is an instrument that determines altitude by measuring the boiling point of water. Since the boiling point of water at standard atmospheric pressure (100°C or 212°F) is a fixed reference point, a hypsometer setup that utilizes the boiling point can also be used to calibrate thermometers at this critical temperature.

Screw Gauge (Micrometer): principle, construction, reading, and applications

  1. The thickness of thin wire can be measured by

    Asked in: Government Dairy Supervisor and Sugar Cane

    1. Vernier Callipers
    2. Screw Gauge
    3. Resonance tube
    4. Spherometer
    Show answer

    Answer: B. Screw Gauge

    Supervisor Examination1 -2023 The choice of measuring instrument depends on the precision required and the dimensions of the object being measured. For extremely small and precise measurements, instruments like the screw gauge are employed.

Stopwatch and principles of time measurement

  1. A clock is started at 12.00 noon. By 10 minutes past 5.00, the hour hand has turned through

    Asked in: BPSC Prelims Exam 66th

    1. 135°
    2. 145°
    3. 155°
    4. 165°
    Show answer

    Answer: C. 155°

    The hour hand moves 360 degrees in 12 hours, which means it moves 30 degrees in one hour or 0.5 degrees per minute. The total time elapsed from 12:00 noon to 5:10 PM is 5 hours and 10 minutes.

  2. A clock is set right at 8 a.m. The clock gains 10 minutes in 24 hours. What will be the true time when the clock indicates 1 p.m. on the following day?

    Asked in: BPSC Prelims Exam 67th Cancelled

    1. 12 noon
    2. 48 minutes past 12 noon
    3. 1 p.m.
    4. 2 p.m.
    Show answer

    Answer: B. 48 minutes past 12 noon

    In 24 hours of true time, the faulty clock shows 24 hours + 10 minutes = 1450 minutes. This means 1450 minutes on the faulty clock correspond to 1440 minutes on the true clock. So, 1 minute on the faulty clock corresponds to 1440/1450 = 144/145 minutes on the true clock. The time elapsed on the faulty clock is 29 hours = 29 60 = 1740 minutes. The true time elapsed is 1740 (144/145) minutes. 1740 / 145 = 12. True time elapsed = 12 144 = 1728 minutes. Convert 1728 minutes to hours and minutes: 1728 / 60 = 28 with a remainder of 48. So, the true time elapsed is 28 hours and 48 minutes from 8 a.m. 8 a.m. + 28 hours 48 minutes = (8 a.m. + 24 hours) + 4 hours 48 minutes = 8 a.m. next day + 4 hours 48 minutes = 12:48 p.m. next day.

  3. A clock is set right at 6 a.m. It gains 10 minutes in 24 hours. What will be the right time when the clock indicates 11 a.m. on the next day?

    Asked in: BPSC Prelims Exam 67th Re Exam

    1. 48 minutes past 10
    2. 50 minutes past 10
    3. 54 minutes past 10
    4. 10 a.m.
    Show answer

    Answer: A. 48 minutes past 10

    - The faulty clock runs faster than the correct clock. - Calculate the time elapsed on the faulty clock. - Use the gain rate to convert the faulty clock time into correct time.

  4. Which one of the following elements is used as a timekeeper in atomic clocks?

    Asked in: UPSC CDS 1 2018

    1. Potassium
    2. Caesium
    3. Calcium
    4. Magnesium
    Show answer

    Answer: B. Caesium

    Caesium-133 is the standard element used as a timekeeper in traditional atomic clocks due to the stable and precisely known frequency of its atomic transition.

  5. Which one of the following correctly describes the principle of the working of an atomic clock?

    Asked in: UPSC CDS 1 2024

    1. Vibration of a small quartz crystal
    2. Simple harmonic motion of atoms inside a crystal
    3. Resonant frequency in cesium (or rubidium) atom
    4. Excitation and de-excitation of hydrogen atoms
    Show answer

    Answer: C. Resonant frequency in cesium (or rubidium) atom

    The principle of an atomic clock relies on the natural, constant frequency associated with transitions between different energy levels of atoms, which are independent of external conditions and thus provide a highly stable frequency standard.

  6. A and B are 2 faulty clocks. A looses 10 minutes for every hour and B gains 10 minutes for every hour. What is the time shown by A when the time shown by B is 7.00 p.m. on the same day, if both clocks were set correct at 12:00 noon that day.

    Asked in: GPSC Prelims CSP 1 2017

    1. 4.30 p.m.
    2. 5.00 p.m.
    3. 5.30 p.m.
    4. 6.00 p.m.
    Show answer

    Answer: B. 5.00 p.m.

    When Clock B shows 7:00 p.m., it means 7 hours have elapsed on Clock B's dial since 12:00 noon. Since Clock B gains time, the actual real time elapsed is less than 7 hours. Let T be the real time elapsed in hours. The ratio of time shown by B to real time is 70/60 = 7/6. So, 7 hours (shown by B) = (7/6) T. This gives T = 6 hours. The real time is 6:00 p.m.

  7. Which one of the following devices is used to measure the intensity of earthquake?

    Asked in: UPPSC Upper Mains 2014

    1. Seismograph
    2. Stethoscope
    3. Comograph
    4. Periscope
    Show answer

    Answer: A. Seismograph

    - A seismograph records seismic waves. - Data from seismographs is used to determine both magnitude and aid in assessing intensity. - It is the primary instrument for objective measurement of earthquake ground motion.

Thermocouples and their applications in temperature measurement

  1. Which of the following instruments is used for measuring very high temperature ?

    Asked in: OPSC CS Prelims 2015

    1. Photometer
    2. Pyrgeometer
    3. Solarimeter
    4. Pyrometer
    Show answer

    Answer: D. Pyrometer

    A pyrometer is a type of remote-sensing thermometer used to measure the temperature of a distant object or surface, typically at high temperatures, by analyzing the thermal radiation emitted.

  2. Which one of the following thermometers is known as pyrometer?

    Asked in: UPPCS Prelims 2016

    1. Thermo-electric thermometers
    2. Radiation thermometers
    3. Gas thermometers
    4. Liquid thermometers
    Show answer

    Answer: B. Radiation thermometers

    Pyrometers are a class of non-contact thermometers that measure the temperature of a surface by detecting the thermal radiation emitted by it. Radiation thermometers are essentially pyrometers. They are commonly used for measuring very high temperatures or temperatures of objects that are inaccessible or hazardous to touch.

  3. A pyrometer is used to measure

    Asked in: UPPSC Upper Mains 2008

    1. atmospheric pressure
    2. humidity
    3. high temperature
    4. density
    Show answer

    Answer: C. high temperature

    A pyrometer is a type of thermometer used for measuring high temperatures, typically above 500°C (932°F). They usually work by sensing the thermal radiation emitted by the object, allowing for non-contact temperature measurement. Atmospheric pressure is measured by a barometer, humidity by a hygrometer, and density by a densitometer or hydrometer.

  4. Phonometer is used to measure which one of the following?

    Asked in: UPPSC Upper Mains 2014

    1. The power of brightness oflight
    2. Extremely high temperature
    3. Frequency of electromagnetic wave
    4. Atmospheric humidity
    Show answer

    Answer: A. The power of brightness oflight

    - A standard Phonometer measures sound intensity. - A Photometer measures light intensity/brightness. - The options provided align with the function of a Photometer, not a Phonometer. - This suggests an error in the question's terminology.

  5. Which type of remote sensing thermometer is used to measure the temperature of distant objects?

    Asked in: Assistant Auditor (Direct) 2021

    1. Trigometer
    2. Ethnometer
    3. Pyrometer
    4. Straincelo
    Show answer

    Answer: C. Pyrometer

    Pyrometers are instruments specifically designed for remote temperature measurement of very hot objects.

Vernier Calipers: principle, construction, reading, and applications

  1. The least count of Vernier Caliper is

    Asked in: ae 2020

    1. 0.01 cm
    2. 0.01 mm
    3. 0.1 cm
    4. 0.001 cm
    Show answer

    Answer: A. 0.01 cm

    ae -2025 The least count of a Vernier caliper is calculated as the difference between the smallest division on the main scale and the smallest division on the Vernier scale. A common configuration gives a least count of 0.01 cm.

Wheatstone Bridge: principle and applications in resistance measurement

  1. The experimental setup in Fig. 5 below measures the value of unknown resistance in two steps: * When $V=24$ V, $r$ is set at $400$ $\Omega$ and $S=80$ $\Omega$, the galvanometer shows a deflection of 30°. * When switch is thrown to position 2, the supply voltage drops down to 12 V and the galvanometer still shows a deflection of 30°. The value of unknown resistance is

    Asked in: GS&EI ElectEngg 14 2024 1601 2025

    1. 80 $\Omega$
    2. 60 $\Omega$
    3. 40 $\Omega$
    4. 20 $\Omega$
    Show answer

    Answer: B. 60 $\Omega$

    GS&EI ElectEngg 14 2024 1601-2025 The problem describes a measurement of unknown resistance using a galvanometer. The key information is that the galvanometer shows the same deflection (30°) despite the supply voltage being halved. This implies a change in the circuit configuration or resistances in "position 2" that compensates for the voltage drop, maintaining the same galvanometer reading. Without the circuit diagram, a precise derivation is impossible, but typical setups for such measurements (e.g., Wheatstone bridge, potentiometer) suggest that specific resistance ratios or balances are involved.

  2. The experimental setup in Fig. 5 below measures the value of unknown resistance in two steps : * When $V = 24$ V, $r$ is set at $400 \Omega$ and $S = 80 \Omega$, the galvanometer shows a deflection of $30^{\circ}$. * When switch is thrown to position 2, the supply voltage drops down to $12$ V and the galvanometer still shows a deflection of $30^{\circ}$. The value of unknown resistance is

    Asked in: GS&EI ElectEngg 14 2024 1601 2025

    1. $80 \Omega$
    2. $60 \Omega$
    3. $40 \Omega$
    4. $20 \Omega$
    Show answer

    Answer: B. $60 \Omega$

    The problem describes an experimental setup for measuring an unknown resistance using a galvanometer. It provides two scenarios with different supply voltages ($V$) and resistance settings ($r$ and $S$), where the galvanometer shows the same deflection ($30^{\circ}$) in both cases. This suggests that the current through the galvanometer, or some quantity proportional to it, remains constant. In resistance measurement experiments like the Wheatstone bridge, the galvanometer is typically used to indicate a balanced condition (null deflection) or a specific level of imbalance. The fact that the voltage is halved while the deflection remains the same implies a specific relationship between the resistances in the circuit. Without the diagram of the experimental setup, a precise derivation is impossible. However, problems of this nature in physics often relate to the principle of ratios in bridges or potentiometers. The answer being one of the given options suggests a unique solution exists for a particular circuit configuration.

  3. In a Schering bridge balance, the following values are obtained : $C_2 = 100 \mu\text{F}, R_3 = 100 \Omega, R_4 = 300 \Omega, C_4 = 0.5 \mu\text{F}, f = 50 \text{ Hz}$ The unknown capacitance $C_1$ and its loss angle $\delta$ are respectively

    Asked in: GS&EI ElectEngg 14 2024 1601 2025

    1. $300 \mu\text{F}, 0.27^{\circ}$
    2. $300 \text{ pF}, 2.7^{\circ}$
    3. $300 \mu\text{F}, 2.7^{\circ}$
    4. $100 \mu\text{F}, 2.5^{\circ}$
    Show answer

    Answer: C. $300 \mu\text{F}, 2.7^{\circ}$

    GS&EI ElectEngg 14 2024 1601-2025 The Schering bridge is used to measure capacitance and dissipation factor. In some configurations, the balance conditions lead to $C_1 = C_2 \frac{R_4} {R_3}$ and $\tan \delta = \omega C_4 R_4$.

  4. In a Schering bridge balance, the following values are obtained : C₂ = 100 µF, R₃ = 100 Ω, C₄ = 0·5 µF, f = 50 Hz The unknown capacitance C₁ and its loss angle δ are respectively

    Asked in: GS&EI ElectEngg 14 2024 1601 2025

    1. 300 µF, 0·27°
    2. 300 pF, 2·7°
    3. 300 µF, 2·7°
    4. 100 µF, 2·5°
    Show answer

    Answer: C. 300 µF, 2·7°

    This question is identical to ID 80852. The Schering bridge is used to measure unknown capacitance. For a balanced Schering bridge, the unknown capacitance $C_1$ and its loss angle $\delta$ are given by the formulas: $C_1 = C_2 \frac{R_4}{R_3}$ $\tan \delta = \omega C_4 R_4$Given values: $C_2 = 100 \mu \text{F}$ $R_3 = 100 \Omega$ $R_4 = 300 \Omega$ $C_4 = 0.5 \mu \text{F}$ $f = 50 \text{ Hz}$Calculate $C_1$: $C_1 = 100 \mu \text{F} \times \frac{300 \Omega}{100 \Omega} = 100 \mu \text{F} \times 3 = 300 \mu \text{F}$.Calculate $\tan \delta$: $\omega = 2\pi f = 2\pi \times 50 = 100\pi \text{ rad/s}$. $\tan \delta = (100\pi \text{ rad/s}) \times (0.5 \times 10^{-6} \text{ F}) \times (300 \Omega)$ $\tan \delta = 100\pi \times 0.04712$.Calculate $\delta$: $\delta = \arctan(0.04712) \approx 2.698^{\circ} \approx 2.7^{\circ}$.Therefore, the unknown capacitance $C_1 = 300 \mu \text{F}$ and its loss angle $\delta = 2.7^{\circ}$. This matches option C.

  5. In a Schering bridge balance, the following values are obtained : $C_2 = 100 \mu F$, $R_3 = 100 \Omega$, $R_4 = 300 \Omega$, $C_4 = 0.5 \mu F$, $f = 50 Hz$ The unknown capacitance $C_1$ and its loss angle $\delta$ are respectively 300 $\mu$F, 0.27° 300 pF, 2.7° 300 $\mu$F, 2.7° 100 $\mu$F, 2.5°

    1. 300 $\mu$F, 0.27°
    2. 300 pF, 2.7°
    3. 300 $\mu$F, 2.7°
    4. 100 $\mu$F, 2.5°
    Show answer

    Answer: C. 300 $\mu$F, 2.7°