Chapter 29, Problem 16P

To determine

The size of energy gap.

Answer to Problem 16P

  $1.94eV$

Explanation of Solution

Given info:

Wavelength is $640nm$ .

Formula used:

The gap energy equals, $E_g=hf=\frac{hc}{\lambda }$

Where,

  $E_g$ is energy gap

  $f$ is frequency

  $\lambda$ is wavelength

  $hf$ is emitted photon

  $h$ is Planck’s constant

  $c$ is speed of light

Calculation:

Photon with the longest wavelength for conduction must have an energy equals to energy gap.

Substitute the given value in $E_g=hf=\frac{hc}{\lambda }$

  $=\frac{\left(1.24\times {10}^{3}eV\cdot nm\right)}{\left(640nm\right)}=1.94eV$

Conclusion: The required value is $1.94eV$ .