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JEE Main
Exam
JEE Main
Subject
Physics
Chapter
Electromagnetic Waves

JEE Main · Physics · Electromagnetic Waves

A laser beam has intensity 2.1 × 10^ 15 ~W / m^2 . The amplitude of...

A laser beam has intensity 2.1×1015 W/m22.1 \times 10^{15} \mathrm{~W} / \mathrm{m}^2. The amplitude of magnetic field in the beam in approximately is

Options

  1. A1.4 T
  2. B4.2 T
  3. C1 T
  4. D1.5 T

Correct answer

B. 4.2 T

Step-by-step solution

I=B022μ0C\mathrm{I}=\frac{\mathrm{B}_0^2}{2 \mu_0} \mathrm{C}⇒2.1×1015=B02×3×1088π×10−7⇒B02=17.64⇒B0=4.2 T\begin{aligned} & \Rightarrow \quad 2.1 \times 10^{15}=\frac{\mathrm{B}_0^2 \times 3 \times 10^8}{8 \pi \times 10^{-7}} \\ & \Rightarrow \quad \mathrm{B}_0^2=17.64 \\ & \Rightarrow \quad \mathrm{B}_0=4.2 \mathrm{~T}\end{aligned}$$
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