Physics (Part-II) (UPSC)

Total Questions: 60

21. The following two items consist of two statements, one labeled as the Assertion (A) and the other as Reason (R). You have to answer these items using the code given below. [2007]

Assertion (A): Radio waves bend in a magnetic field.

Reason (R): Radio waves are electromagnetic in nature.

(a) Both A are R are true and R is the correct explanation of A
(b) Both 4 and R are true but R is not a correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

Correct Answer: (d) A is false but R is true

Solution:Assertion (A) states that "Radio waves bend in a magnetic field," which is incorrect. Radio waves, being electromagnetic waves, typically travel in straight lines through a vacuum and are not directly affected by magnetic fields in terms of bending. Instead, they are influenced by the medium's properties. Reason (R) asserts that "Radio waves are electromagnetic in nature," which is correct. Given these evaluations, Assertion (A) is false, and Reason (R) is true. Therefore, the correct answer is that Assertion (A) is false but Reason (R) is true.

22. Which one of the following types of waves are used in a night vision apparatus? [2009]

(a) Radio waves
(b) Microwaves
(c) Infra-red waves
(d) None of the above

Correct Answer: (c) Infra-red waves

Solution:Night Vision as referenced here is that technology that provides us with the miracle of vision in total darkness and the improvement of vision in low light environments. Infra-red waves are used in night vision apparatus.

23. Consider the figure given below and answer the item that follows: [2011-11]

In the figure shown above, O*P_{1} and O*P_{2} are two plane mirrors kept perpendicular to each other. S is the direction of a beam of light falling on the mirror O*P_{V} The direction of the reflected beam of light from the mirror O*P_{2} will be:

(a) Perpendicular to the direction S.
(b) At 45 deg to the direction S.
(c) Opposite and parallel to the direction S.
(d) At 60 deg to the direction S.

Correct Answer: (c) Opposite and parallel to the direction S.

Solution:

In the above figure, dotted line shows the reflected beam of light from mirror OP2.

24. Consider the following phenomena: [2013-1]

1. Size of the sun at dusk.

2. Colour of the sun at dawn

3. Moon being visible at dawn

4. Twinkle of stars in the sky

5. Polestar being visible in the sky

Which of the above are optical illusions?

(a) 1, 2 and 3
(b) 3, 4 and 5
(c) 1, 2 and 4
(d) 2, 3 and 5

Correct Answer: (c) 1, 2 and 4

Solution:Size of the Sun at dusk is an optical illusion because of atmospheric refraction. Colour of the sun appears yellow due to scattering whereas pure sunlight is white in colour. Twinkling of stars is an optical illusion. Air whirlpools make the stars twinkle.

25. Rainbow is produced when sunlight falls on drops of rain. Which of the following physical phenomena are responsible for this? [2013-1]

1. Dispersion

2. Refraction

3. Internal reflection

Select the correct answer using the codes below.

(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3

Correct Answer: (d) 1, 2 and 3

Solution:Formation of rainbow involves all dispersian, refraction and internal reflection.

26. During a thunderstorm, the thunder in the skies is produced by the [2013-1]

1. meeting of cumulonimbus clouds in the sky

2. lightning that separates the nimbus clouds

3. violent upward movement of air and water particles

Select the correct answer using the codes given below.

(a) 1 only
(b) 2 and 3
(c) 1 and 3
(d) None of the above produces the thunder

Correct Answer: (d) None of the above produces the thunder

Solution:Thunderstorms result from the rapid upward movement of warm, moist air. They can occur inside warm, moist air masses and at fronts. As the warm, moist air moves upward, it cools, condenses, and forms cumulonimbus clouds that can reach heights of over 20 km (12.45 miles). The thunderstorms are associated with the cumulonimbus clouds. These clouds normally form on warm sunny days but they can also be found on cold front. But this question is asking about the Thunder i.e. the sound produced. The lightning generates between 100 million and 1 billion volts of electricity and can heat the air to around 50K°F. The rapid expansion causes the shock waves. Thunder happens because the lightning would heat the air at huge temperatures and the air expands so fast that it make a loud clap of thunder.

27. The following item consists of two statements, one labeled as the Assertion (A) and the other as Reason (R). You have to answer this item using the code given below. [1996]

Assertion (A): Transformer is useful for stepping up or stepping down voltages.

Reason (R): Transformer is a device used in D.C. circuits, In the context of the above two statements, which one of the following is correct?

(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not a correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

Correct Answer: (c) A is true but R is false

Solution:A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors-the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a voltage in the secondary winding. By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) or voltage to be "stepped up" by making greater than N_{p} or "stepped down" by making N * less than N_{p} Here tilde N_{p} represents number of turns in primary winding. N_{s} represents the number of turns in secondary winding. As it is clear from principle involved that transformer can be used to step up and step down A.C. voltage only. This device can not be used for D.C. voltage as its working is based on the change of magnetic flux with varying current.

28. Domestic electrical wiring is basically a: [1996]

(a) series connection
(b) parallel connection
(c) combination of series and parallel connections
(d) series connection within each room and parallel connection elsewhere

Correct Answer: (b) parallel connection

Solution:In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents through each component. The wiring for most homes is parallel .In parallel circuit each branch receives equal current. If one branch in the circuit is broken, electric current will still flow in other branches.

29. Which one of the following is paramagnetic in nature? [1997]

(a) Iron
(b) Hydrogen
(c) Oxygen
(d) Nitrogen

Correct Answer: (c) Oxygen

Solution:Paramagnetism occurs in substances that have unpaired electrons, which are attracted to an external magnetic field. Among the options given: Iron: Has unpaired electrons in its d-orbitals, making it paramagnetic. Hydrogen: Has one proton with one unpaired electron, making it paramagnetic.

Oxygen: Has two unpaired electrons in its molecular form (O), making it paramagnetic.

Nitrogen: Has all electrons paired in its molecular form (N.), making it diamagnetic.

Therefore, correct answer is Oxygen. Oxygen is paramagnetic due to having two unpaired electrons in its molecular form.

30. A fuse is used in mains electric supply as a safety device. Which one of the following statements about the fuse is correct? [1998]

(a) It is connected in parallel with the main switch
(b) It is made mainly from silver alloys
(c) It must have a low melting point
(d) It must have very high resistance

Correct Answer: (c) It must have a low melting point

Solution:A fuse is a type of sacrificial overcurrent protection device. Its essential component is a metal wire or strip that melts when too much current flows. Short circuit, overload or device failure is often the reason for excessive current.

The resistance of the element used in fuse generates heat due to the current flow. It has low melting point so that it melts when a short-circuit or overloading takes place.

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