JEE Main & Advanced Physics EM Waves JEE PYQ-Electro Magnetic Waves

  • question_answer
    A red LED emits light at 0.1 watt uniformly around it. The amplitude of the electric field of the light at a distance of 1m from the diode is:                                    [JEE MAIN 2015]

    A) 5.48 V/m

    B) 7.75 V/m

    C) 1.73 V/m

    D) 2.45 V/mions /

    Correct Answer: D

    Solution :

    [d] \[I=\frac{E_{0}^{2}}{2c{{\mu }_{0}}}\]
    \[\frac{P}{4\pi {{r}^{2}}}=\frac{E_{0}^{2}}{2c{{\mu }_{0}}}\]
    \[E=\frac{P2c{{\mu }_{0}}}{4\pi {{r}^{2}}}\]
    \[E=\frac{0.1\times 2\times 3\times {{10}^{-8}}\times 4\pi \times {{N}^{-1}}}{4\pi }\]
    \[=\sqrt{6}=2.45\]


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