Measuring Instruments and Scales

1. The equipment used to measure the electrical current in a closed circu

The equipment used to measure the electrical current in a closed circuit is

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Galvanometer.
Ammeter.
Voltmeter.
Compass needle.
This question was previously asked in
UPSC CISF-AC-EXE – 2021
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An ammeter is the standard instrument used to measure the electric current flowing through a circuit. It is connected in series with the component through which the current is to be measured.
– An ammeter measures electric current.
– It must be connected in series in a circuit.
– A voltmeter measures voltage (potential difference).
– A galvanometer detects small currents and their direction.
Ammeter is derived from “ampere meter,” as current is measured in amperes (A). Ideal ammeters have very low internal resistance so as not to significantly affect the current they are measuring. Galvanometers can be used as components to build ammeters and voltmeters with appropriate shunts or series resistances.

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2. Automobiles are fitted with a device that shows the distance travelled

Automobiles are fitted with a device that shows the distance travelled. Such a device is known as

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Speedometer
Cathetometer
Odometer
Lactometer
This question was previously asked in
UPSC CISF-AC-EXE – 2017
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Different devices are used in automobiles to measure various parameters:
– Speedometer: Measures the instantaneous speed of the vehicle.
– Odometer: Measures the total distance traveled by the vehicle.
– Tachometer: Measures the engine’s rotational speed (RPM).
– Fuel gauge: Indicates the amount of fuel in the tank.

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A Cathetometer is a laboratory instrument used to measure vertical distances precisely. A Lactometer is an instrument used to check the purity of milk by measuring its density.

Therefore, the device fitted in automobiles that shows the distance traveled is an 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.
Modern odometers are typically digital, while older vehicles used mechanical odometers with rotating number wheels. The term “odometer” comes from the Greek words ‘hodos’ (way or path) and ‘metron’ (measure). Trip meters are usually integrated with the odometer and can be reset to measure distances for specific journeys.

3. Consider the following actions: 1. Detection of car crash/collision

Consider the following actions:

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  • 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?

1 and 2 only
2 and 3 only
1 and 3 only
1, 2 and 3
This question was previously asked in
UPSC IAS – 2023
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The correct option is D, indicating that the function of a gyroscope is used in all three actions.
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.
2. **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.
IMUs provide six degrees of freedom (6-DOF) motion sensing (three axes of acceleration, three axes of angular velocity). This combined data allows for robust tracking of movement and orientation in 3D space, enabling these and many other features in various devices.

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4. Which one of the following instruments is used for measuring moisture

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

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Hydrometer
Hygrometer
Hypsometer
Pycnometer
This question was previously asked in
UPSC CAPF – 2017
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A Hygrometer is used for measuring moisture content of air.
– 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.
Different types of hygrometers exist, including mechanical hygrometers, electrical hygrometers (using resistance or capacitance), and dew-point hygrometers. They are essential tools in meteorology, HVAC systems, and various industrial and scientific applications where humidity control is important.

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5. A Barometer kept in an elevator reads 760 mm when the elevator is at r

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:

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760 mm
> 760 mm
Zero
This question was previously asked in
UPSC CAPF – 2016
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When the elevator moves upward with increasing speed (i.e., it is accelerating upwards), the apparent weight of objects inside the elevator increases. A barometer measures the pressure exerted by the column of air above it. In the upward accelerating frame of reference, the effective acceleration of gravity is (g + a), where g is the standard acceleration due to gravity and a is the upward acceleration of the elevator. The pressure exerted by the air column is proportional to this effective gravity. Therefore, the air pressure measured by the barometer will be higher than the normal atmospheric pressure (760 mm Hg) measured when the elevator is at rest.
This question tests the understanding of apparent weight and pressure measurement in accelerating reference frames.
If the elevator were moving downwards with increasing speed (accelerating downwards), the apparent weight and measured pressure would decrease (reading < 760 mm). If the elevator were moving at a constant velocity (up or down), the acceleration would be zero, and the reading would remain 760 mm. If the elevator were falling freely (a = -g), the apparent weight and pressure would be zero.

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6. If a scientist reads an ambient temperature 273 K in the laboratory, w

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

0 degree Fahrenheit
32 degrees Fahrenheit
99 degrees Fahrenheit
– 100 degrees Fahrenheit
This question was previously asked in
UPSC CAPF – 2014
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The correct answer is 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.

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So, 273 K is equivalent to 32°F. This corresponds to the freezing point of water.

The exact freezing point of water is 273.15 K or 0°C or 32°F. The value 273 K is a common approximation used in many problems.

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7. The presence of magnetic field can be determined using which one of th

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

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Ammeter
Voltmeter
Magnetic needle
Motor
This question was previously asked in
UPSC NDA-2 – 2022
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The presence of a magnetic field can be determined using a 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.
An Ammeter measures electric current. A Voltmeter measures electric potential difference (voltage). A Motor converts electrical energy into mechanical energy using the principle of magnetic force on a current-carrying wire, but it’s not primarily an instrument for *detecting* a magnetic field’s presence in general. Other instruments for measuring magnetic fields include magnetometers, but a magnetic needle is a simple and fundamental tool for detection.

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8. The instrument used for detecting the presence of electric current in

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

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Refractometer
Galvanometer
Viscometer
Diffractometer
This question was previously asked in
UPSC NDA-2 – 2020
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The correct answer is (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).
A refractometer is used to measure the refractive index of a substance. A viscometer is used to measure the viscosity of a fluid. A diffractometer is used to study the diffraction of radiation (like X-rays or electrons) by a material, often to determine its crystal structure.

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9. Radioactivity is measured by

Radioactivity is measured by

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GM Counter
Polarimeter
Calorimeter
Colorimeter
This question was previously asked in
UPSC NDA-2 – 2017
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Radioactivity is the spontaneous emission of radiation (alpha, beta, gamma rays) from unstable atomic nuclei. A Geiger-Muller counter (GM Counter) is a widely used instrument specifically designed to detect and measure ionizing radiation, which is characteristic of radioactive decay. It works by detecting the ionization caused by radiation passing through a gas-filled tube.
– Radioactivity involves the emission of ionizing radiation.
– A GM Counter is an instrument that detects ionizing radiation.
A Polarimeter measures the rotation of polarized light by optical active substances. A Calorimeter measures heat flow or thermal energy. A Colorimeter measures the absorbance or transmission of light by a solution at specific wavelengths to determine concentration or color properties. None of these are used to measure radioactivity. Other instruments for measuring radioactivity include scintillation counters and semiconductor detectors.

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10. Which one of the following statements is correct ?

Which one of the following statements is correct ?

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The measurement of mass taken by a spring weighing balance is correct at the place where the spring balance is calibrated for
The measurement of mass taken by a spring weighing balance is correct at all places
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 cannot be used to measure mass at any place
This question was previously asked in
UPSC NDA-2 – 2016
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The correct answer is C. A spring balance measures weight, which is the force exerted by gravity on a mass (Weight = mass × g).
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.
Beam balances (like a physical balance) compare the mass of an unknown object with known standard masses. They compare masses directly by balancing torques, and thus their measurement is independent of the local acceleration due to gravity ‘g’. A spring balance, however, measures force (weight) and infers mass based on the calibrated relationship between spring extension and weight at a specific ‘g’.

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