11.29 The work function for the following metals is given:

Na: 2.75 eV; K: 2.30 eV; Mo: 4.17 eV; Ni: 5.15 eV. Which of these metals will not give photoelectric emission for a radiation of wavelength 3300 Å from a He-Cd laser placed 1 m away from the photocell? What happens if the laser is brought nearer and placed 50 cm away ?

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    Answered by

    Payal Gupta | Contributor-Level 10

    4 months ago

    11.29 Wavelength of the radiation, λ = 3300 Å = 3300 × 10 - 10 m

    Speed of light, c = 3 × 10 8 m/s

    Planck’s constant, h = 6.626 × 10 - 34 Js

    The energy of the incident radiation is given as:

    E = h c λ

    = 6.626 × 10 - 34 × 3 × 10 8 3300 × 10 - 10 = 6.024 × 10 - 19 J = 6.024 × 10 - 19 1.6 × 10 - 19 eV = 3.765 eV

    It can be observed that the energy of incident radiation is greater than the work function of Na and K only. Mo and Ni having more work function will not show the photoelectric emission.

    If the source of light is brought near the photocells and placed 50 cm away from them, then the intensity of radiation will increase, but it will not affect the energy of the radiation. Hence, the result will be the same as before. However, the p

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