Question

Photon having wavelength 12.4 nm was allowed to strike a metal plate having work function 25 eV. The maximum kinetic energy of photoelectrons emitted in eV is:

• A. 75 eV
• B. 65 eV
• C. 78 eV
• D. 84 eV

Answer 1

Answer: (A)

75 eV

According to photoelectric effect, electron from outermost shell can be knocked out by irradiating the material surface with a threshold energy called work function $E_0$. Rest of the energy given converts into kinetic energy of the released electron.

$Totalenergy=kineticenergy+workfunction$................(i)

Relating $\lambda$ and energy using equation:

$E=\frac{hc}{\lambda }$

where, h= $4.136\times {10}^{-15}eV.s$ and c=$3\times {10}^{17}nm/s$ and $\lambda$ = $12.4nm$

After putting all the above values in the energy equation we get,

Energy of the incident photon, E=$100eV$

From the equation (i),

$E=K.E.+\varphi$

$100eV=K.E.+25eV$

Therefore, $K.E.=75eV$.

Option A is the correct answer.