Dual Nature of Radiation and Matter · Question 36

A parallel beam of fast moving electrons is incident normally on a narrow slit. A fluorescent screen is placed at a large distance from the slit. If the speed of the electrons is increased, which of the following statements is correct ?

1. The angular width of the central maximum will decrease.
2. The angular width of the central maximum will be unaffected.
3. Diffraction pattern is not observed on the screen in the case of electrons.
4. The angular width of the central maximum of the diffraction pattern will increase.

The wavelength e of an electron and p of a photon of same energy E are related by

1. p e
2. p 1 e
3. p e2
4. p e

For photoelectric emission from certain metal the cutoff frequency is . If radiation of frequency 2 impinges on the metal plate, the maximum possible velocity of the emitted electron will be (m is the electron mass)

1. 2h m
2. 2 h m
3. h (2m)
4. h m

A source of light is placed at a distance of 50 cm from a photo cell and the stopping potential is found to be V0. If the distance between the light source and photo cell is made 25 cm, the new stopping potential will be :

1. V0/2
2. V0
3. 4V0
4. 2V0

The de-broglie wavelength of neutrons in thermal equilibrium at temperature T is

1. 3.08 T A
2. 0.308 T A
3. 0.0308 T A
4. 30.8 T A

If the momentum of an electron is changed by P, then the de Broglie wavelength associated with it changes by 0.5\%. The initial momentum of electron will be

1. 200 P
2. 400 P
3. P200
4. 100 P

Two radiations of photons energies 1 eV and 2.5 eV, successively illuminate a photosensitive metallic surface of work function 0.5 eV. The ratio of the maximum speeds of the emitted electrons is

1. 1 : 4
2. 1 : 2
3. 1 : 1
4. 1 : 5

A 200 W sodium street lamp emits yellow light of wavelength 0.6 . Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is

1. 1.5 1020
2. 6 1018
3. 62 1020
4. 3 1019

Monochromatic radiation emitted when electron in hydrogen atom jumps from first excited to the ground state irradiates a photosensitive material. The stopping potential is measured to be 3.57 V. The threshold frequency of the material is

1. 4 1015 Hz
2. 5 1015 Hz
3. 1.6 1015 Hz
4. 2.5 1015 Hz

An -particle moves in a circular path of radius 0.83 cm in the presence of a magnetic field of 0.25 Wb/m2. The de Broglie wavelength associated with the particle will be

1. 1 A
2. 0.1 A
3. 10 A
4. 0.01 A