Q. The rest mass of an electron as well as that of positron is $0.51\ MeV$. When an electron and positron are annihilate, they produce gamma-rays of wavelength(s)
A) $0.012\ \mathring{\mathrm{A}}$
B) $0.024\ \mathring{\mathrm{A}}$
C) $0.012\ \mathring{\mathrm{A}}\ $to$\ \infty$
D) $0.024\ \mathring{\mathrm{A}}\ $to$\ \infty$
Explanation
(a) Since electron and positron annihilate
$\lambda = \frac{hc}{E_{Total}} = \frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{(0.51 + 0.51) \times 10^{6} \times 1.6 \times 10^{- 19}}$
$= 1.21 \times 10^{- 12}m = 0.012\mathring{\mathrm{A}}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.