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

The figure shows a plot of photo current versus anode potential for a photo sensitive surface for three difference radiations. Which one of the following is a correct statement?

1. Curves a and b represent incident radiations of different frequencies and different intensities

2. Curves a and b represent incident radiations of same frequency but of different intensities 

3. Curves b and c represent incident radiations of different frequencies and different intensities

4. Curves b and c represent incident radiations of same frequency having same intensity