Monochromatic radiation emitted when electron on 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. $4\times {10}^{15}Hz$                               

2. $5\times {10}^{15}Hz$

3.$\mathrm{ 1}.6\times {10}^{15}Hz$                           

4. $2.5\times {10}^{15}Hz$

In the Davisson and Germer experiment, the velocity of electrons emitted from the electron gun can be increased by

1. increasing the filament current

2. decreasing the filament current

3. decreasing the potential difference between the anode and filament

4. increasing the potential difference  between the anode and filament

A radioactive nucleus of mass M emits a photon of frequency $\nu$ and the nucleus recoils. The recoil energy will be:

1. ${\mathrm{h}}^2{\mathrm{\nu }}^2/2 {\mathrm{Mc}}^2$

2. zero

3. h$\nu$

4. ${\mathrm{Mc}}^2-\mathrm{h\nu }$

Photoelectric emission occurs only when the incident light has more than a certain minimum 

1. wavelength

2. intensity

3. frequency

4. power

The threshold frequency for a photo-sensitive metal is $3.3\times {10}^{14} \mathrm{Hz}.$ If the light of frequency $8.2\times {10}^{14} \mathrm{Hz}$ is incident on this metal, the cut-off voltage for the photo-electric emission is nearly:

1. 2 V                                        2. 3 V

3. 5 V                                         4. 1 V