Question

a) A scientist is trying to eject electrons from a metal by shining a light on it. The electrons are bound inside the metal need energy of 2.0 eV to escape. Which wavelength will eject electrons? a. 350 nm b. 420 nm C. any of these d. 600 nm e. none of these

Answer 1

Given:

work function = W = 2 eV

Now, let's calculate the threshold wavelength for the metal first, then the wavelength of light which is less than the threshold is eligible to emit electrons from the surface of the metal.

$W=\frac{hc}{\lambda_{o}}$ [$\lambda_{o}$ = threshold wavelength]

$\Rightarrow \lambda_{o}=\frac{hc}{W}$

$=\frac{6.63*10^{-34}*3*10^{8}}{2*1.6*10^{-19}}=621.56*10^{-9}m=621.56nm$

As the wavelengths of light given in a, b and d are all less than the threshold wavelength, so any of these wavelengths will eject electrons from the metal surface.

Therefore, the correct option is c. [answer]