The difference between kinetic energies of photoelectrons emitted from a surface by light of wavelength 2500 $\stackrel{0}{A}$ and 500 $\stackrel{0}{A}$ will be

1. 1.61 J

2. 2.47 J

3. 3.96 J

4. $3.9\times {10}^{-19} J$

When a point source of light is 1 m away from a photoelectric cell, the photoelectric current is found to be I mA. If the same source is placed at 4 m from the same photoelectric cells, the photoelectric current (in mA) will be:

1. $\frac{I}{16}$

2. $\frac{I}{4}$

3. $4\mathrm{I}$

4. $16 \mathrm{I}$
 

The work function of tungsten and sodium is 4.5 eV and 2.3 eV respectively. If the threshold wavelength $\lambda$ for sodium is 5460 $\stackrel{0}{A}$, the value of $\lambda$ for tungsten is:
 

1. 2791 $\stackrel{0}{A}$

2. 3260 $\stackrel{0}{A}$

3. 1925 $\stackrel{0}{A}$

.4 1000 $\stackrel{0}{A}$

A photon of energy E ejects a photoelectrons from a metal surface whose work function is $W_0$. If this electron enters into a uniform magnetic field of induction B in a direction perpendicular to the field and describes a circular path of radius r, then the radius r is, given by:

1. $\sqrt{\frac{2m (W_0-E)}{eB}}$

2. $\sqrt{\frac{2e (E-W_0)}{mB}}$

3. $\sqrt{\frac{2m (E-W_0)}{eB}}$

4. $\sqrt{\frac{2m{W}_0}{eB}}$

A metal surface of work function 1.07 eV is irradiated with light of wavelength 332 nm. The retarding potential required to stop the escape of photoelectrons is:

1. 1.07 V

2. 2.66 V

3. 3.7 V

4. 4.81 V

If the work function for a certain metal is $3.2\times {10}^{-19} J$ and it is illuminated with light of frequency $v=8\times {10}^{14} Hz$, the maximum kinetic energy of the photoelectron would be:

1. $2.1\times {10}^{-19} J$

2. $3.2\times {10}^{-19} J$

3. $5.3\times {10}^{-19} J$

4. $8.5\times {10}^{-19} J$

Ultraviolet light of wavelength 300 nm and intensity 1.0 $W{m}^{-2}$ falls on the surface of a photosensitive material. If one percent of the incident photons produce photoelectrons, then the number of photoelectrons emitted from an area of 1.0 $c{m}^2$ of the surface is nearly

1. $9.61\times {10}^{14} s^{-1}$

2. $4.12\times {10}^{13} s^{-1}$

3. $1.51\times {10}^{12} s^{-1}$

4. $2.13\times {10}^{11} s^{-1}$

A metal surface is illuminated by a light of given intensity and frequency to cause photoemission. If the intensity of illumination is reduced to one-fourth of its original value, then the maximum kinetic energy of the emitted photoelectrons would become:

1. four times the original value

2. twice the original value

3. 1/6th of the original value

4. unchanged

Ultraviolet radiation of 6.2 eV falls on an aluminium surface (work function 4.2 eV). The kinetic energy in joule of the fastest electron emitted is approximately.

1. $3\times {10}^{-21}$

2. $3.2\times {10}^{-19}$

3. $3\times {10}^{-17}$

4. $3\times {10}^{-15}$

Radiations of two different photonic energies, twice and ten times the work function of metal are incident on the metal surface successively. The ratio of maximum velocities of photoelectrons emitted in two cases is:

1. 1:2

2. 1:4

3. 1:3

4. 1:1