Q35
General SciencePhysics
A photon of frequency 50 Hz possesses _____ J energy. ($h$: Planck's constant, $c$: speed of light in vacuum)
- a.$50h$
- b.$\frac{h}{50}$
- c.$\frac{hc}{50}$
- d.$50c$
Answer: (A) $50h$
The energy of a photon is given by Planck's relation $E = h\nu$, where $\nu$ is the frequency. Putting $\nu = 50$ Hz gives $E = 50h$ joules, option A. Option C is the trap: $E = \frac{hc}{\lambda}$ is the form of the same relation in terms of wavelength, so $\frac{hc}{50}$ would be right only if 50 were the wavelength in metres; options B and D are dimensionally wrong. Facts to remember: $h = 6.626 \times 10^{-34}$ J s, photon energy rises with frequency (gamma rays highest, radio waves lowest), and 50 Hz is also the frequency of India's AC mains supply.