When the energy of the incident radiation is increased by `20 %` , kinetic energy of the photoelectrons emitted from a metal surface increased from `0.5 eV to 0.8 eV`. The work function of the metal is

Options

A. `0.65 eV`
B. `1.0 eV`
C. `1.3 eV`
D. `1.5 eV`

Answer

b

Explanation

According to Einstein's photoelectron equation
`K_(max)=hv-phi_(0) :. 0.5=hv-phi_(0)......(i)`
and `0.8=h(v+20/100v)-phi_(0)`
`1.2hv-phi_(0).......(ii)`
Multiplying (i) by `1.2`, we get
`0.6=1.2 hv-1.2 phi_(0).......(iii)`
Subtracting (iii) from (ii), we get
`0.2=0.2 phi_(0)` or `phi_(0)=1eV`