Microwaves And Radar

NCERT Class 12, Chapter 8 (Electromagnetic Waves) notes that microwaves have short wavelengths, roughly from 1 mm to about 30 cm, allowing them to travel in well-defined straight beams and to reflect efficiently from objects such as aircraft and vehicles. The short wavelength is important because efficient reflection requires the reflecting object to be comparable in size to or larger than the wavelength, a condition metals and vehicles easily satisfy for microwaves. Radar relies on sending out microwave pulses and timing their reflections to find distance, while speed guns use the Doppler shift of reflected microwaves to measure velocity; both applications depend on this directional propagation and strong reflection. The option that microwaves are completely absorbed by the atmosphere is wrong, because significant absorption would prevent any echo from returning to the receiver. The claim that microwaves have longer wavelengths than radio waves is false, since radio waves occupy the longer-wavelength region of the spectrum. The statement that microwaves carry more energy per photon than gamma rays is incorrect, as gamma rays are far higher in frequency and photon energy. A plausibility check based on the physics of echo-based ranging confirms that straight-line travel and strong reflection are the key useful properties, making that option correct.