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 : 2
2. 1 : 1 
3. 1 : 5 
4. 1 : 4

When monochromatic radiation of intenisty I falls on a metal surface, the number of
photoelectron and their maximum kinetic energy are N and T respectively. If the intensity of radiation is 2I, the number of emitted electrons and their maximum kinetic energy are respectively-

1. 2N and T

2. 2N and 2T

3. N and T

4. N and 2T

A 5 W  emits monochromatic light of wavelength 5000 Å. When placed 0.5 m away, it liberates photoelectrons from a photosensitive metallic surface. When the source is moved 1.0 m away, the number of photoelectrons liberated is reduced by a factor of?

1. 4

2. 8

3. 16

4. 2