# JEE Mains Question 8th April 2018 Set A Physics Part 7 Download all the papers for 2019 Exam

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Q-23 The angular width of the central maximum in a single slit diffraction pattern is. The width of the slit is. The slit is illuminated by monochromatic plane waves. If another slit of same width is made near it, young’s fringes can be observed on a screen placed at a distance of 50 cm from the slits. If the observed fringe width is 1 cm, what is slit separation distance?

(I.e. distance between the centres of each slit.)

Options:-

1.

2.

3.

4.

Answer: 1

Explanation:-

In, Y dse,

Q-24 An electron from various excited states of hydrogen atom emit radiation to come to the ground state. Let be the de Broglie wavelength of the electron in the state and the ground state respectively. Let be the wavelength of the emitted photon in the transition from the state to the ground state. For large n,

Options:-

1.

2.

3.

4.

Answer: 3

Explanation:-

For emitted photon,

Q-25 If the series limit frequency of the Lyman series is, then the series limit frequency of the Pfund series is:

Options:-

1.

2.

3.

4.

Answer: 4

Explanation:-

Q-26 It is found that if a neutron suffers an elastic collinear collision with deuterium at rest, fractional loss of its energy is; while for its similar collision with carbon nucleus at rest, fractional loss of energy is pc. The values of are respectively:

Options:-

1.

2.

3.

4.

Answer: 1

Explanation:-

Since collision is elastic,

………………….. (i)

Fractional loss in kinetic energy of neutron,

So, ATQ;