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NEET-XII-Physics

08: Electromagnetic Waves

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  • #12
    About 5% of the power of a 100 W light bulb is converted to visible radiation. What is the average intensity of visible radiation
    (a) at a distance of 1 m from the bulb?
    (b) at a distance of 10 m?

    Assume that the radiation is emitted isotropically and neglect reflection.
    (b) at a distance of 10 m?

    Assume that the radiation is emitted isotropically and neglect reflection.
    (a) at a distance of 1 m from the bulb?
    (b) at a distance of 10 m?

    Assume that the radiation is emitted isotropically and neglect reflection.
    (b) at a distance of 10 m?

    Assume that the radiation is emitted isotropically and neglect reflection.
    Ans : Power rating of bulb, P = 100 W

    It is given that about 5% of its power is converted into visible radiation.

    Power of visible radiation,



    Hence, the power of visible radiation is 5W.
    (a) Distance of a point from the bulb, d = 1 m

    Hence, intensity of radiation at that point is given as:


    (b) Distance of a point from the bulb, d1 = 10 m

    Hence, intensity of radiation at that point is given as:


    (b) Distance of a point from the bulb, d1 = 10 m

    Hence, intensity of radiation at that point is given as:


    (a) Distance of a point from the bulb, d = 1 m

    Hence, intensity of radiation at that point is given as:


    (b) Distance of a point from the bulb, d1 = 10 m

    Hence, intensity of radiation at that point is given as:


    (b) Distance of a point from the bulb, d1 = 10 m

    Hence, intensity of radiation at that point is given as:


  • #12-a
    at a distance of 1 m from the bulb?
    (b) at a distance of 10 m?

    Assume that the radiation is emitted isotropically and neglect reflection.
    Ans : Distance of a point from the bulb, d = 1 m

    Hence, intensity of radiation at that point is given as:


    (b) Distance of a point from the bulb, d1 = 10 m

    Hence, intensity of radiation at that point is given as:


  • #12-b
    at a distance of 10 m?

    Assume that the radiation is emitted isotropically and neglect reflection.
    Ans : Distance of a point from the bulb, d1 = 10 m

    Hence, intensity of radiation at that point is given as: