JEE Main · 2023 · 12 Apr 2023 · Shift 1 · EM Waves

Optical communication uses infrared and visible light, whose frequencies ($\sim 10^{14}\text{Hz}$) are far higher than those of the microwaves used in radar ($\sim 10^9\text{–}10^{10}\text{Hz}$). Since $\lambda =\frac{c}{f}$, a higher frequency means a shorter wavelength, so the waves used for optical communication have shorter wavelengths than microwaves; Assertion A is false. The energy of a photon is $E=hf$, and infrared radiation has a higher frequency than microwaves, so infrared is more energetic; Reason R is true. Therefore Assertion A is false but Reason R is true.