Question

Find the photon energy in units of electron volts of electromagnetic waves of wavelength $40 m ?$

• A. $3 \times 10^{-8} eV$
• B. $3.1 \times 10^{-8} eV$
• C. $3.2 \times 10^{-8} eV$
• D. $3.3 \times 10^{-8} eV$

Answer 1

Answer: (B)

$E =\frac{ hc }{\lambda}=\frac{6.6 \times 10^{-34} \times 3 \times 10^{8}}{40} J$
$E =\frac{6.6 \times 10^{-34} \times 3 \times 10^{8}}{40 \times 1.6 \times 10^{-19}} eV$
$=\frac{19.8 \times 10^{-7}}{64}$
$=0.30 \times 10^{-7} eV$
$E=3.1 \times 10^{-8} eV$