Question

What is the mass of photon of sodium light having a wavelength of $5890\mathring{A}$? (Given $h=6.6\times {10}^{-27}erg-sec$)

• A. $3.735\times {10}^{-29}g$
• B. $3.735\times {10}^{-33}g$
• C. $1.57\times {10}^{-33}g$
• D. $3.735\times {10}^{-31}g$

Answer 1

The correct option is B $3.735\times {10}^{-33}g$

The de-Broglie's equation is $\lambda =\frac{h}{mu}$
Here, $\lambda$ is the wavelength of the photon, m is the mass of the photon, h is Planck's constant and u is the velocity of the photon.
The above equation is rearranged to $m=\frac{h}{\lambda \times u}$
$u=3\times {10}^{10}cm/sec$ and $\lambda =5890\mathring{A}=5.89\times {10}^{-5}cm$
Substitute values in the above equation.
$m=\frac{6.6\times {10}^{-27}ergsec}{5.89\times {10}^{-5}cm\times 3\times {10}^{10}cm/s}=3.735\times {10}^{-33}g$