Question

Light of wavelength 5000 Å falls on a sensitive plate with photoelectric work function of 1.9 eV. The kinetic energy of the photoelectron emitted will be
1. 1.24 eV
2. 2.48 eV
3. 0.58 eV
4. 1.16 eV

Answer 1

Correct Answer - Option 3 : 0.58 eV

CONCEPT: 

Photoelectric Effect:

• When the light of a sufficiently small wavelength is incident on the metal surface, electrons are ejected from the metal instantly. This phenomenon is called the photoelectric effect.​
• Einstein’s equation of photoelectric equation:

⇒ KEmax = hν - ϕo

Where h = Planck's constant, ν = frequency of incident radiation, ϕo = work function, and KE = maximum kinetic energy of electrons.

CALCULATION : 

Given - λ = 5000 Å and ϕ₀ = 1.9eV

• The equation of kinetic energy is given by

⇒ KEmax = hν - ϕ₀

Substitute the value \(\nu = \frac{C}{\lambda }\)

\(⇒ KE_{max} = \dfrac{hc}{λ}- \phi_{0}\)

Substituting the given values in the above equation

\(⇒ KE_{max} = \dfrac{6.626\times 10^{-34} \times 3\times 10^{8}}{5000\times 10^{-10}\times 1.6\times 10^{-19}}- 1.9\)

⇒ KE_max = 2.48 - 1.9  = 0.58 eV

• Hence, option 3 is the answer