Question

A radar sends an electromagnetic signal of electric field (E 0) = 2.25 V/m and magnetic field (B 0) = 1.5 × 10-8 T which strikes a target on line of sight at a distance of 3 km in a medium. After that, a part of signal (echo) reflects back towards the radar with same velocity and by same path. If the signal was transmitted at time t = 0 from radar, then after how much time echo will reach to the radar?

• A. 2.0 × 10–5 s
• B. 4.0 × 10-5 s
• C. 1.0 × 10-5 s
• D. 8.0 × 10-5 s

Answer 1

Answer: (B)

4.0 × 10-5 s

Answer 2

The correct answer is (B) : 4.0 × 10–5 s
E 0 = 2.25 V/m
B 0 = 1.5 × 10–8T
$⇒ \frac{E_0}{B_0} = 1.5 × 10^8$ m/s
⇒ Refractive index = 2
Distance to be travelled = 6 km
Time taken
$=\frac{6 × 10^3}{1.5 × 10^8} = 4 × 10^{-5}$ s