A radar sends a short microwave pulse towards an aircraft. The pulse reflected by the aircraft reaches the radar \(2\times10^{-4}\ \mathrm{s}\) after it was sent. The distance of the aircraft from the radar is (Take the speed of the pulse in air as \(3\times10^{8}\ \mathrm{m\,s^{-1}}\))
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 30 km
Microwaves are electromagnetic waves, so the pulse moves with the speed \( c \). In the time \( t \) it goes to the aircraft and comes back. So it covers twice the distance \( d \).
\( t=2\times10^{-4}\ \mathrm{s} \)
\( \begin{aligned} 2d &= ct \\ d &= \frac{ct}{2} \\ &= \frac{3\times10^{8}\times2\times10^{-4}}{2} \\ &= 3\times10^{4}\ \mathrm{m} \\ &= 30\ \mathrm{km} \end{aligned} \)
NCERT (2026-27):
Summary – “Light is an electromagnetic wave; c is, therefore, also the speed of light. Electromagnetic waves other than light also have the same velocity c in free space.”