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A 100W sodium lamp radiates energy unifo...

A 100W sodium lamp radiates energy uniformly in all directions. The lamp is located at the centre of a large sphere that absorbs all the sodium light which is incident on it. The wavelength of the sodium light is 589nm. (a) What is energy associated per photon with the sodium light? (b) At what rate are photons delivered to the sphere?

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(a) Energy associated per photon with the sodium light is,
`E=(hc)/lambda=(6.63xx10^(-34)xx3xx10^(8))/(589xx10^(-9))=3.38xx10^(-19)J , (b) n=P/E=100/(3.38xx10^(-19))=3.0xx10^(20)"photons"//s`
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A 100W sodium lamp radiates energyuniformly in all directions. The lamp is located at the centre of a large sphere that absorbs all the sodium light which is incident on it. The wavelength of the sodium light is 589 nm. (a) what is the energy per photon associated with the sodium light? (b) At what rate are the photons delivered to the sphere ?

(a) A 100 W sodium Lamp radiates energy uniformly in all directions. The Lamp is located at the centre of a large sphere , that absorbs all the sodium of a large sphere , that absorbs all the sodium light which is incident on it . The wavelength of the sodium light is 589 nm (i) What is the energy associated per photon with the sodium light ? (ii) At what rate are the photons delivered to the sphere ? (b) Light of frequency 7.21 xx10^(14) Hz is incident on a metal surface . Electrons with a maximum speed of 6.0xx10^(5) ms^(-1) are ejected from the surface What is the threshold frequency for photo emission of electron ? Given , h= 6.63xx10^(-34) Js , m_c=9.1xx10^(-310 Kg

Knowledge Check

  • A 160 watt infrared source is radiating light of wavelength 50000Å uniformly in all directions. The photon flux at a distance of 1.18 m is of the order of -

    A
    `10 m^(-2)s^(-1)`
    B
    `10^(10)m^(-2)s^(-1)`
    C
    `10^(15)m^(-2)s^(-1)`
    D
    `10^(20)m^(-2)s^(-1)`

  • If the wavelength of light emitted by a sodium vapour lamp is 5893 A then the numebr of photons emitted in 5 hour by a 50 W lamp will be

    A
    `7.4 xx10^(20)` photons
    B
    `4.46 xx10^(22)` photons
    C
    `2.7 xx10^(24)` photons
    D
    `5.4 xx10^(23)` photons

  • If mean wavelength of light radiated by 100 W lamp is 5000 Å , then number of photons radiated per second are

    A
    `3 xx 10^(23)`
    B
    `2.5 xx 10^(22)`
    C
    `2.5 xx 10^(20)`
    D
    `5 xx 10^(17)`

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