JEE Main & Advanced Physics Wave Optics / तरंग प्रकाशिकी Question Bank Critical Thinking

  • question_answer
    A lamp emits monochromatic green light uniformly in all directions. The lamp is 3% efficient in converting electrical power to electromagnetic waves and consumes 100W of power. The amplitude of the electric field associated with the electromagnetic radiation at a distance of 10m from the lamp will be

    A)            1.34 V/m                                

    B)            2.68 V/m

    C)            5.36 V/m                                

    D)            9.37 V/m

    Correct Answer: A

    Solution :

               \[{{S}_{av}}=\frac{1}{2}{{\varepsilon }_{0}}cE_{0}^{2}=\frac{P}{4\pi {{R}^{2}}}\] Þ \[{{E}_{0}}=\sqrt{\frac{P}{2\pi {{R}^{2}}{{\varepsilon }_{0}}C}}\]          \[=\sqrt{\frac{3}{2\times 3.14\times 100\times 8.85\times {{10}^{-12}}\times 3\times {{10}^{8}}}}\]           = 1.34 V/m


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