Physics

Problem

In a photoelectric experiment a parallel beam of monochromatic light with power of

200 \text{ W}

is incident on a perfectly absorbing cathode of work function

6.25 \text{ eV}

. The frequency of light is just above the threshold frequency so that the photoelectrons are emitted with negligible kinetic energy. Assume that the photoelectron emission efficiency is

100\%

. A potential difference of

500 \text{ V}

is applied between the cathode and the anode. All the emitted electrons are incident normally on the anode and are absorbed. The anode experiences a force

F = n \times 10^{-4} \text{ N}

due to the impact of the electrons. The value of

n

is ______. Mass of the electron

m_e = 9 \times 10^{-31} \text{ kg}

and

1.0 \text{ eV} = 1.6 \times 10^{-19} \text{ J}

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