A radar sends an electromagnetic signal of electric field $\left(E_0\right)=2.25 \mathrm{V} {\mathrm{m}}^{-1}$ and magnetic field $\left(B_0\right)=1.5\times {10}^{-8} \mathrm{T}$ 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 $t=0$ from radar, then after how much time echo will reach to the radar?

• A

  $2.0\times {10}^{-5} \mathrm{s}$
• Correct answer
  B

  $4.0\times {10}^{-5} \mathrm{s}$
• C

  $1.0\times {10}^{-5}\mathrm{s}$
• D

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

Hence, the correct answer is option: 'B'.