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

The photoelectric threshold wavelength for a metal surface is 6600 Å. The work function for this is 
(1) 1.87 V                             

(2) 1.87 eV

(3) 18.7 eV                             

(4) 0.18 eV

Photoelectric effect was successfully explained first by
(1) Planck               

(2) Hallwash

(3) Hertz                 

(4) Einstein