JEE Main 2022 · 28 Jun · Shift 1 · Physics Q41

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PhysicsSingle correct+4 / -1Question 41 of 90

A radar sends an electromagnetic signal of electric field $(E_0)=2.25$ V/m and magnetic field $(B_0)=1.5\times10^{-8}$ 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?

2.0\times10^{-5}

4.0\times10^{-5}

1.0\times10^{-5}

8.0\times10^{-5}

Answer and worked solution

Official answer: B

Speed in the medium. $v=\dfrac{E_0}{B_0}=\dfrac{2.25}{1.5\times10^{-8}}=1.5\times10^8$ m s $^{-1}$ .

Round trip. $\dfrac{6000}{1.5\times10^8}=4.0\times10^{-5}$ s.

(B)

Topics:Properties of EM waves

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JEE Main 2022 · 28 Jun · Shift 1, Physics question 41