JEE MAIN - Physics (2022 - 28th June Morning Shift - No. 11)
A radar sends an electromagnetic signal of electric field (E0) = 2.25 V/m and magnetic field (B0) = 1.5 $$\times$$ 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?
2.0 $$\times$$ 10$$-$$5 s
4.0 $$\times$$ 10$$-$$5 s
1.0 $$\times$$ 10$$-$$5 s
8.0 $$\times$$ 10$$-$$5 s
Explanation
E0 = 2.25 V/m
B0 = 1.5 $$\times$$ 10$$-$$8 T
$$ \Rightarrow {{{E_0}} \over {{B_0}}} = 1.5 \times {10^8}$$ m/s
$$\Rightarrow$$ Refractive index = 2
Distance to be travelled = 6 km
Time taken $$ = {{6 \times {{10}^3}} \over {1.5 \times {{10}^8}}} = 4 \times {10^{ - 5}}$$ s
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