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  • A radar sends an electromagnetic signal of electric field <img alt="\left(\mathrm{E}_{\mathrm{o}}\right)=2.25 \mathrm{~V} / \mathrm{m}" src="/latex-image/?%5Cleft%28%5Cmathrm%7BE%7D_%7B%5Cmathrm%7B

A radar sends an electromagnetic signal of electric field \left(\mathrm{E}_{\mathrm{o}}\right)=2.25 \mathrm{~V} / \mathrm{m} and magnetic field \left(\mathrm{B}_{\mathrm{o}}\right)=1.5 \times 10^{-8} \mathrm{~T} which strikes a target on line of sight at a distance of 3 \mathrm{~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 \mathrm{t}=0 from radar, then after how much time echo will reach to the radar?
 

Option: 1

2.0 \times 10^{-5} \mathrm{~s}


Option: 2

4.0 \times 10^{-5} \mathrm{~s}


Option: 3

1.0 \times 10^{-5} \mathrm{~s}


Option: 4

8.0 \times 10^{-5} \mathrm{~s}


Answers (1)

best_answer

Speed of wave will be

\mathrm{v =\frac{E_{0}}{B_{0}}} \\

\mathrm{=\frac{2.25}{1.5 \times 10^{-8}}=\frac{2.25}{1.5} \times 10^{8} }\frac{\mathrm{m}}{\mathrm{s}}

\mathrm{\operatorname{time} =\frac{6 \mathrm{~km}}{\left(\frac{2.25}{1.5}\right) \times 10^{8}}} \\

\mathrm{=\frac{6 \times 1.5 }{2.25} \times\frac{10^{3}}{10^{8}}} \\

\mathrm{=4 \times 10^{-5} \mathrm{sec}}

Hence the correct option is 2

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