In a photo cell, the photo-electrons emission takes place
(1) After ${10}^{-1}$ sec on incident of light rays

(2) After ${10}^{-3}$ sec on incident of light rays

(3) After ${10}^{-6}$ sec on incident of light rays

(4) After ${10}^{-8}$ sec on incident of light rays

When light falls on a metal surface, the maximum kinetic energy of the emitted photo-electrons depends upon

(1) The time for which light falls on the metal

(2) Frequency of the incident light

(3) Intensity of the incident light

(4) Velocity of the incident light

The electrons are emitted in the photoelectric effect from a metal surface 

(1) Only if the frequency of the incident radiation is above a certain threshold value

(2) Only if the temperature of the surface is high

(3) At a rate that is independent of the nature of the metal

(4) With a maximum velocity proportional to the frequency of the incident radiation

The work function of a metal is \(4.2 ~\text{eV}\), its threshold wavelength will be:
1. \(4000~\mathring{\text{A}}\)                   
2. \(3500~\mathring{\text{A}}\)
3. \(2955~\mathring{\text{A}}\) 
4. \(2500~\mathring{\text{A}}\)

The number of photo-electrons emitted per second from a metal surface increases when:

The work function of metal is 1 eV. Light of wavelength 3000 Å is incident on this metal surface. The velocity of emitted photo-electrons will be
(a) 10 m/sec                           (b) $1\times {10}^3$ m/sec
(c) $1\times {10}^4$ m/sec                     (d) $1\times {10}^6$ m/sec

The work function of a metal is $1.6\times {10}^{-19}$ J. When the metal surface is illuminated by the light of wavelength 6400 Å, then the maximum kinetic energy of emitted photo-electrons will be
(Planck's constant = $6.4\times {10}^{-34 }\mathrm{Js}$) 
(a) $14\times {10}^{-19} \mathrm{J}$                 (b) $2.8\times {10}^{-19} \mathrm{J}$ 
(c) $1.4\times {10}^{-19} \mathrm{J}$                (d) $1.4\times {10}^{-19} \mathrm{eV}$

Ultraviolet radiations of 6.2 eV falls on an aluminium surface (work function 4.2 eV ). The kinetic energy in joules of the fastest electron emitted is approximately
1. $3.2\times {10}^{-21}$             

2. $3.2\times {10}^{-19}$

3. $3.2\times {10}^{-17}$             

4. $3.2\times {10}^{-15}$

The work function for tungsten and sodium are 4.5 eV and 2.3 eV respectively. If the threshold wavelength $\mathrm{\lambda }$ for sodium is 5460 Å, the value of $\mathrm{\lambda }$ for tungsten is

(1) 5893 Å                   

(2) 10683 Å

(3) 2791 Å                   

(4) 528 Å