Question

The threshold wavelength for certain metal is . When light of wavelength $\frac{{\lambda }_0}{2}$ is incident on it, the maximum velocity of photo electrons is ${10}^{6}m/s$. If the wavelength of incident light is changed to $\frac{{\lambda }_0}{5}$ the maximum velocity of photo electrons is

• A. 2.5 x10⁶ m/ s
• B. 3 x10⁶ m/ s
• C. 2 x10⁶ m/ s
• D. 1.5 x10⁶ m/ s

Answer 1

The correct option is C

2 x10⁶ m/ s

$K{E}_1=\frac{2hc}{{\lambda }_0}-\frac{hc}{{\lambda }_0}=\frac{hc}{{\lambda }_0};K{E}_2=\frac{5hc}{{\lambda }_0}-\frac{hc}{{\lambda }_0}=\frac{4hc}{{\lambda }_0};{\left[\frac{v_1}{v_2}\right]}^2=\frac{1}{4};v_2=2v_1$