Verified Solution • 2025–26 Session moderate

QJEEM24Ph2ff8: JEE Main 2024 Physics - Class 12 JEEM24Ph2ff8 Solution: In the given electromagnetic wave , intensity of the associated …

In the given electromagnetic wave Ey=600sin⁡(ωt−kx)Vm−1\mathrm{E}_{\mathrm{y}}=600 \sin (\omega t-\mathrm{kx}) \mathrm{Vm}^{-1} , intensity of the associated light beam is (in W/m2\mathrm{W} / \mathrm{m}^2 : (Given ϵ0=9×10−12C2 N−1 m−2\epsilon_0=9 \times 10^{-12} \mathrm{C}^2 \mathrm{~N}^{-1} \mathrm{~m}^{-2} )

Multiple Choice Options

  • A 486
  • B 729
  • C 243
  • D 972

Step-by-Step Verified Solution

To find the intensity of the given electromagnetic wave, we need to use the formula for the intensity of an electromagnetic wave:

I=12ϵ0cE02I = \frac{1}{2} \epsilon_0 c E_0^2

where:

  • II is the intensity in W/m2\mathrm{W} / \mathrm{m}^2
  • ϵ0\epsilon_0 is the permittivity of free space, given as 9×10−12C2 N−1 m−29 \times 10^{-12} \mathrm{C}^2 \mathrm{~N}^{-1} \mathrm{~m}^{-2}
  • cc is the speed of light in vacuum, approximately 3×108 m/s3 \times 10^8 \mathrm{~m/s}
  • E0E_0 is the peak electric field, given as 600Vm−1600 \mathrm{Vm}^{-1}

Now, substitute these values into the formula:

I=12×9×10−12×3×108×(600)2I = \frac{1}{2} \times 9 \times 10^{-12} \times 3 \times 10^8 \times (600)^2

Simplify the expression step-by-step:

I=12×9×10−12×3×108×360000I = \frac{1}{2} \times 9 \times 10^{-12} \times 3 \times 10^8 \times 360000

First, calculate 9×3×3600009 \times 3 \times 360000 :

I=12×9.72×10−4×360000I = \frac{1}{2} \times 9.72 \times 10^{-4} \times 360000

Combine 9 and 3 into 27, giving you:

I=13.5×10−4×360000I = 13.5 \times 10^{-4} \times 360000

Then, calculate the multiplication:

I=13.5×36I = 13.5 \times 36

Finally, multiply the remaining values:

I=486×10−4I = 486 \times 10^{-4}

The final value is:

The intensity, II , is 486 W/m2\mathrm{W} / \mathrm{m}^2 . Therefore, the correct option is:

Option A: 486

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