Question

Choose the correct answer from the alternatives given.
The photon energy in units of $eV$ for electromagnetic waves of wavelength $2cm$ is then

• A. $2.5\times {10}^{-19}$
• B. $5.2\times {10}^{16}$
• C. $3.2\times {10}^{-16}$
• D. $6.2\times {10}^{-5}$

Answer 1

The correct option is D $6.2\times {10}^{-5}$

Given: The wavelength of the electromagnetic wave is $2cm$.

To find: The photon energy in terms of $eV$.

The energy of the photon of particular wavelength is given by:

$E=\frac{hc}{\lambda }=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{2\times {10}^{-2}}\Rightarrow 9.9\times {10}^{-24}J$

Convert the energy into $eV$.

$E\left(eV\right)=\frac{9.9\times {10}^{-24}}{1.6\times {10}^{-19}}eV=6.2\times {10}^{-5}eV$

Option $\left(D\right)$ is correct.