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JEE Main 202330 JanuaryEvening Shift
Exam
JEE Main
Year
2023
Date
30 January
Shift
Evening Shift
Subject
Physics
Chapter
Dual Nature of Matter

JEE Main 2023 · 30 January · Evening Shift · Physics · Dual Nature of Matter

A point source of 100W emits light with 5 % efficiency. At a...

A point source of 100W100W emits light with 55 % efficiency. At a distance of 5m5m from the source, the intensity produced by the electric field component is:

Options

  1. A12πWm2\dfrac{1}{2\pi}\dfrac{W}{{m}^{2}}
  2. B140πWm2\dfrac{1}{40\pi}\dfrac{W}{{m}^{2}}
  3. C110πWm2\dfrac{1}{10\pi}\dfrac{W}{{m}^{2}}
  4. D120Wm2\dfrac{1}{20}\dfrac{W}{{m}^{2}}

Correct answer

B. 140πWm2\dfrac{1}{40\pi}\dfrac{W}{{m}^{2}}

Step-by-step solution

Total power emitted =100×5100=5W= 100 \times \dfrac{5}{100} = 5W

Now intensity due to electric field will be half of the total intensity. Therefore,

IE=12×powerarea=12×54π×52{I}_{E} = \dfrac{1}{2} \times \dfrac{\text{power}}{\text{area}} = \dfrac{1}{2} \times \dfrac{5}{4\pi \times {5}^{2}}

=140πWm2= \dfrac{1}{40\pi}\dfrac{W}{{m}^{2}}

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