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JEE Main 202228 JuneMorning Shift
Exam
JEE Main
Year
2022
Date
28 June
Shift
Morning Shift
Subject
Physics
Chapter
Waves and Sound

JEE Main 2022 · 28 June · Morning Shift · Physics · Waves and Sound

A radar sends an electromagnetic signal of electric field ( E _ 0 )...

A radar sends an electromagnetic signal of electric field (E0)=2.25Vm−1andmagneticfield(B0)=1.5×10−8T\left({E}_{0}\right) = 2 . 25V{m}^{- 1} and magnetic field \left({B}_{0}\right) = 1 . 5 \times {10}^{- 8}T which strikes a target on line of sight at a distance of 3km3km 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=0t = 0 from radar, then after how much time echo will reach to the radar?

Options

  1. A2.0×10−5s2 . 0 \times {10}^{- 5}s
  2. B4.0×10−5s4 . 0 \times {10}^{- 5}s
  3. C1.0×10−5s1 . 0 \times {10}^{- 5}s
  4. D8.0×10−5s8 . 0 \times {10}^{- 5}s

Correct answer

B. 4.0×10−5s4 . 0 \times {10}^{- 5}s

Step-by-step solution

The speed of light is given by,

c=E0B0=2.251.5×10−8=1.5×108ms−1c = \dfrac{{E}_{0}}{{B}_{0}} = \dfrac{2 . 25}{1 . 5 \times {10}^{- 8}} = 1 . 5 \times {10}^{8}{ms}^{- 1}

Therefore, time taken for the echo will be,

t=2dc=6×1031.5×108=4×10−5st = \dfrac{2d}{c} = \dfrac{6 \times {10}^{3}}{1 . 5 \times {10}^{8}} = 4 \times {10}^{- 5}s

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