Long Answer TypeWhat is photoelectric effect ? With the help of a suitable graph show the variation of photo current with,
(i) The intensity of incident radiation.
(ii) Voltage applied between cathode and anode.
(iii) Frequency of incident radiation.
The potential difference across an x-ray tube is 12.4 kV and the current through the filament is 2 mA.
Calculate :
(i) the number of electrons striking per second on the anode.
(ii) The speed with which the electron strikes the target.
(iii) The shortest wavelength of X-rays emitted.
i) Number of electrons striking per second on the anode is,
V = 124 kV,
i = 2 mA = 2 x 10-3 A
We know that,
q = ne and
q = it
This implies,
it = ne
Therefore, 
ii) Speed with which the electron strikes the target is,
We know that, 
iii) Shortest wavelength of X-rays emitted is,
Here E - eV ...(i)
and 
From eqn. (i) and (ii), we get 
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