Question

The photon energy in units of $eV$ for electromagnetic waves of wavelength $2\, cm$ is

• 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

Answer: (D)

As $E = \frac{hc}{\lambda}$
$ = \frac{6.6 \times 10^{-34} \times3\times 10^{8} }{2 \times 10^{-2}}$
$ = 9.9 \times 10^{-24}\,J$
$= \frac{9.9 \times 10^{-24}}{1.6 \times 10^{-19}} eV$
$ = 6.2 \times 10^{-5}\,eV$