Q. The $21\ cm$ radio wave emitted by hydrogen in interstellar space is due to the interaction called the hyperfine interaction is atomic hydrogen. the energy of the emitted wave is nearly
A) $10^{- 17}Joule$
B) $1\ Joule$
C) $7 \times 10^{- 8}Joule$
D) $10^{- 24}Joule$
Explanation
(d) $E = \frac{hc}{\lambda} = \frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{21 \times 10^{- 2}} = 0.94 \times 10^{- 24} = 10^{- 24}J$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.