Physics (CDS-Solved Paper)

Total Questions: 50

41. Infrared, visible and ultraviolet radiations/light have different properties. Which one of the following statements related to these radiations/light is not correct? [Evening Shift-2017 (II)]

Correct Answer: (c) The photon energy of visible light is more than that of infrared light.
Solution:

Wavelength of visible light lies in the range of 400 nm to 700 nm. Wavelength of a infrared light lies in the range of 10³ nm to 10⁶ nm. As energy is inversely proportional to the wavelength. Hence, photon energy of visible light is less than that of infrared light.

42. After using for some time, big transformers get heated up. This is due to the fact that

1. current produces heat in the transformers.
2. hysteresis loss occurs in the transformers.
3. liquid used for cooling gets heated.
Select the correct answer using the codes given below

Correct Answer: (c) 1 and 2
Solution:

The transformers get heated up due to the following reasons :
(i) The current flowing through the wire of resistance (R) produces a heat (I²R .
(ii) The magnetisation of the core produces heat due to hysteresis loss.
Transformer oil or insulating oil that, is stable at high temperatures and has excellent electrical insulating properties are used as coolant.

43. A person is standing on a frictionless horizontal ground. How can he move by a certain distance on this ground? [Evening Shift-2017 (II)]

Correct Answer: (a) By sneezing
Solution:

A person is standing on a frictionless horizontal ground can move by a certain distance on this ground due to reaction caused by sneezing. The person cannot run, jump or roll on the frictionless surface.

44. Joule-Thomson process is extremely useful and economical for attaining low temperature. The process can be categorised as [Evening Shift-2017 (II)]

Correct Answer: (c) adiabatic process
Solution:

In Joule-Thomson process, the temperature remains low. Thus, heat content of the process can be taken as constant. Therefore, the process can be categorised as adiabatic process.

45. Ultrasonic waves are produced by making use of [Evening Shift-2017 (II)]

Correct Answer: (c) piezoelectric material
Solution:

Piezoelectric effect is used in the production of ultrasonic sound waves. Therefore, piezoelectric material, i.e. compound of sodium or potassium can be utilised for the production of ultrasonic waves.

46. A person throws an object on a horizontal frictionless plane surface. It is noticed that, there are two forces acting on this object – (i) gravitational pull and (ii) normal reaction of the surface. According to the third law of motion, the net resultant force is zero. Which one of the following can be said for the motion of the objects ? [Evening Shift-2017 (II)]

Correct Answer: (d) The object will move with constant velocity.
Solution:

Two forces acting on the object are gravitational pull of the earth and the normal reaction of the surface. These forces are equal in magnitude and opposite in directions. Thus, net force on the object is zero and the object will move with constant velocity.

47. Consider the following statements :

1. The chain reaction process is used in nuclear bombs to release a vast amount of energy, but in nuclear reactors, there is no chain reaction.
2. In a nuclear reactor, the reaction is controlled, while in nuclear bombs, the reaction is uncontrolled.
3. In a nuclear reactor, all operating reactors are ‘critical’, while there is no question of ‘critically’ in case of a nuclear bomb.
4. Nuclear reactors do not use moderators, while nuclear bombs use them.
Which of the above statements about operational principles of a nuclear reactor and a nuclear bomb is/are correct?

Correct Answer: (b) 2 and 3
Solution:

Chain reaction is the principle of nuclear reactors, while uncontrolled chain reaction is the principle of atom bomb.
In nuclear reactor, the reaction is controlled by control material like as cadmium rod or moderator.
In a nuclear reactor, all operating reactors are critical, while there is no question of critically in case of a nuclear bomb.
Hence, statements 2 are 3 are correct.

48. When a piece of pure silicon is doped with aluminium, then [Morning Shift-2017 (I)]

Correct Answer: (c) the doped silicon piece will become p-type
Solution:

The aluminium atom has three electrons in its outer shell, which is one less than needed to form valence bonds with four nearby silicon atoms.
So, one covalent bond with Si-atom is left incomplete due to deficiency of one electron because of this a p-type semiconductor is formed.
This type of semiconductor, hence formed by doping of trivalent impurity atoms, i.e. Al is known as p-type semiconductor.

49. Suppose voltage V is applied across a resistance R. The power dissipated in the resistance is P. Now, the same voltage V is applied across a parallel combination of three equal resistors each of resistance R. Then, the power dissipated in the second case will be [Morning Shift-2017 (I)]

Correct Answer: (b) 3P
Solution:

50. Which one of the following is not a semiconductor? [Morning Shift-2017 (I)]

Correct Answer: (c) Quartz
Solution:

A semiconductor means a solid substance that allows heat or electricity to pass through it in particular conditions. Here, Si, Ge, GaAs (Gallium arsenide) are semiconductors while quartz is the second most abundant mineral in earth’s continental crust, after feldspar. Its crystal structure is a continuous framework of SiO₄ (silicon- oxygen tetrahedra) with each oxygen being shared between two tetrahedra, giving the overall  chemical formula of SiO₂.