Physics (Part-2) (CDS-Solved Paper)

Total Questions: 50

1. A parallel plate capacitor, with air in between the plates, has capacitance C. Now, the space between the two plates of the capacitor is filled with a dielectric of dielectric constant 7. Then, the value of the capacitance will become [Morning Shift-2017 (I)]

Correct Answer: (c) 7C
Solution:


2. For which one of the following does the centre of mass lie outside the body? [Morning Shift-2017 (I)]

Correct Answer: (c) A ring
Solution:

The  centre of mass  of a rigid body is a point at a fixed position with respect to the body, where whole mass of the body is supposed to be concentrated. For a ring, the centre of mass lies at the geometrical centre, where there is no matter, so it lies outside.

3. Consider the electromagnetic radiations having wavelengths 200 nm, 500 nm and 1000 nm. Which of the following wavelength(s) can make visual sensation to a human eye? [Morning Shift-2017 (I)]

Correct Answer: (c) 500 nm
Solution:

Visible light is the light that we can see and helps us to see things around us. The range of visible wavelengths is 400 to 700 nm. So, wavelength 500 nm lies in visible region.

4. A copper wire of radius r and length l has a resistance of R. A second copper wire with radius 2r and length l is taken and the two wires are joined in a parallel combination. The resultant resistance of the parallel combination of the two wires will be [Morning Shift-2017 (I)]

Correct Answer: (d)
Solution:



5. A parallel plate capacitor of capacitance C₁ is made using two gold plates. Another parallel plate capacitor of capacitance C₂ is made using two aluminium plates with same plate separation and all the four plates are of same area. If ρg and ρa are respectively the electrical resistivities of gold and aluminium, then which one of the following relations is correct? [Morning Shift-2017 (I)]

Correct Answer: (d)
Solution:

6. A photon of X-ray has energy of 1 keV. A photon of visible radiation has energy of 3 eV. In this context, which one of the following statement(s) is/are not correct? [Morning Shift-2017 (I)]

Correct Answer: (c) The speeds of both the photons in vacuum are different.
Solution:

In physics, electromagnetic radiation (EM radiation or EMR) refers to the waves (or their quanta, photons) of the electromagnetic field, propagating (radiating) through space carrying electromagnetic radiant energy. Electromagnetic radiation consists of electromagnetic waves, which are synchronised oscillations of electric and magnetic fields that propagate at the speed of light through a vacuum. Hence, speeds of a photon of energy 1 keV and another photon of energy 3eV are same in vacuum. Frequency of X-ray photon is higher than any other photon. Hence, option (c) is incorrect.

7. The optical phenomenon that is primarily responsible for the observation of rainbow on a rainy day is [Morning Shift-2017 (I)]

Correct Answer: (c) dispersion
Solution:

One of nature’s most splendid masterpieces is the rainbow. A rainbow is an excellent demonstration of the dispersion of light and one more piece of evidence that visible light is composed of a spectrum of wavelengths, each associated with a distinct colour. Hence, option (c) is correct.

8. Which one of the following statement(s) is/are not correct? [Morning Shift-2017 (I)]

Correct Answer: (d) The characteristics of cathode rays depend upon the nature of the gas present in the cathode ray tube.
Solution:

Cathode ray tube is a vacuum tube that contains one or more electron guns and a phosphorescent screen and is used to display images. It modulates, accelerates and defects electron beam on to the screen to create the images. The characteristics of cathode rays does not depend upon the nature of the gas present in the cathode ray tube. Since, it is consist of accelerated electron.

9. In total internal reflection, the light travels from [Morning Shift-2017 (I)]

Correct Answer: (d) denser to rarer medium and it occurs with loss of intensity
Solution:

In total internal reflection, light travels from an optically denser medium to a rarer medium at the interface. It is partly reflected back into the same medium and partly refracted back to the second medium. The intensity of the reflected and refracted rays do not remain constant but reflection occurs with loss of intensity.

10. The energy of a photon, whose momentum is 10 MeV/c, where c is the speed of light, is given by [Morning Shift-2017 (I)]

Correct Answer: (a) 10 MeV
Solution: