Measuring Instruments and Scales

11. Numerically two thermometers, one in Fahrenheit scale and another in C

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

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– 40°
0°
– 273°
100°
This question was previously asked in
UPSC NDA-1 – 2021
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The temperature at which both the Fahrenheit and Celsius scales read the same numerical value is -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.
Water freezes at 0°C (32°F) and boils at 100°C (212°F). These fixed points are different on the two scales, but there is one point where they intersect.

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12. Which one of the following devices is used to measure atmospheric pres

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

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Ammeter
Barometer
Potentiometer
Lactometer
This question was previously asked in
UPSC NDA-1 – 2018
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A barometer is the device specifically used to measure atmospheric pressure.
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.
An ammeter measures electric current. A potentiometer measures electrical potential difference (voltage). A lactometer is a hydrometer used to test the purity or density of milk.

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13. Which of the following can be used to determine the polarity of an unm

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

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An electroscope
Iron filings
A compass
Another unmarked bar magnet
This question was previously asked in
UPSC Geoscientist – 2022
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A compass is essentially a small magnet (needle) that is free to rotate and align itself with the Earth’s magnetic field. The red or North-seeking pole of the compass needle points towards the Earth’s magnetic North pole. If you bring an unmarked bar magnet near the compass, the compass needle will be either attracted or repelled by the poles of the bar magnet. By observing which pole of the compass (whose polarity is known) is attracted or repelled by each end of the unmarked magnet, you can determine the polarity of the unmarked magnet. Like poles repel, and opposite poles attract.
– 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.
An electroscope detects electric charge, not magnetism. Iron filings visualize magnetic field lines but don’t directly label poles. Bringing two unmarked magnets together allows observation of attraction/repulsion, but without knowing the polarity of at least one, you cannot label the poles definitively, although you can confirm they are magnets and identify pairs of like and unlike poles.

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

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

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Ammeter
Motor
Voltmeter
Generator
This question was previously asked in
UPSC CDS-2 – 2022
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An ammeter is specifically designed and used to measure the flow of electric current (measured in Amperes) through a point in a circuit.
– An ammeter is connected in series within the circuit to measure the total current flowing through that part of the circuit.
A voltmeter is used to measure the potential difference (voltage) across two points in a circuit. A motor converts electrical energy into mechanical energy. A generator converts mechanical energy into electrical energy.

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15. Which one of the following correctly describes the principle of the wo

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

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Vibration of a small quartz crystal
Simple harmonic motion of atoms inside a crystal
Resonant frequency in cesium (or rubidium) atom
Excitation and de-excitation of hydrogen atoms
This question was previously asked in
UPSC CDS-1 – 2024
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The correct answer is C. An atomic clock works based on the precise and stable resonant frequency of atoms, typically Cesium or Rubidium.
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.
Modern atomic clocks define the second based on the radiation frequency corresponding to the transition between two specific hyperfine levels of the ground state of the Cesium-133 atom. Rubidium clocks are also used, offering portability at slightly lower accuracy than Cesium primary standards. Quartz crystal vibrations are used in quartz clocks, which are less accurate than atomic clocks.

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16. Which one of the following elements is used as a timekeeper in atomic

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

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Potassium
Caesium
Calcium
Magnesium
This question was previously asked in
UPSC CDS-1 – 2018
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Atomic clocks utilize the precise frequency of electromagnetic radiation absorbed or emitted by atoms during an electron transition between energy levels. Caesium-133 atoms are most commonly used as the primary standard for defining the second in modern atomic clocks. The official SI definition of the second is based on the frequency of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the Caesium-133 atom.
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.
While Caesium clocks are the most widespread standard, other elements like Rubidium are also used, and advanced research is ongoing using elements like Strontium and Ytterbium in optical lattice clocks which offer even higher precision.

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