Raisa asked in Science & MathematicsPhysics · 6 months ago


The given is the graph of - frequency of light incident on a metal plate vs kinetic energy of emitted electron.

i. What is the threshold frequency?

ii. If light of 1000Å wavelength is incident on the plate, will electron be emitted?

Attachment image

1 Answer

  • 6 months ago

    E_k = h*f - W

    So the slope of the line is h and we are looking for the f-intercept f0.

    Using the pair E_k = 5×10^15 and f = 1.2 * 1.6×10^-19 J

    Definition of slope

    h = (E_k - 0) / (f - f0)

    f0 = f - (E_k / h) =

    = 2.1×10^15 Hz

    1000 Å is frequency of 3×10^15 Hz which is more than f0 so it is enough energy per photon to trigger the effect.

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