Question

The energy of photon in an electromagnetic wave is of the order $15\text{keV}$. To which part of the spectrum does it belong?

• A. Ultraviolet rays
• B. $\gamma -$rays
• C. $X-$rays
• D. Infrared rays

Answer 1

The correct option is C $X-$rays

We know that, energy of an electromagnetic wave is given by,

$U=\frac{hc}{\lambda }$

$\Rightarrow \lambda =\frac{hc}{U}=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{15\times {10}^3\times 1.6\times {10}^{-19}}$

$\Rightarrow \lambda =8.25\times {10}^{-11}\text{m}$

$\Rightarrow \lambda \sim {10}^{-11}\text{m}$

For $X-$ rays, wavelength range is ${10}^{-9}-{10}^{-11}$.

Therefore, the electromagnetic wave belongs to $X-$rays spectrum.

Hence, option $\left(C\right)$ is the correct answer.