# Dual Nature of Radiation and Matter - III

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Compton Shift:
It is the phenomenon of increase in the wavelength of X-ray photons which occurs when these radiations are scattered on striking an electron. The difference in the wavelength of scattered and incident photons is called Compton shift, which is given by

Where f is the angle of scattering of the X-ray photon and m0 is the rest mass of the
electron.

Charge and Mass of an Electron by Thompson’s Method:
a) J. J. Thomson devised an experiment to determine the velocity (v) and the ratio of
the charge (e) to the mass (m) i.e., e/m of cathode rays .

c) In the region where they are applied perpendicular to each other and to the direction of motion of cathode rays,

Force due to electric field, FE = Force due to magnetic field FB,

Where V = Potential difference between the two electrodes (i.e., P and Q), d = distance between the two electrodes, R = radius of circular arc in the presence of magnetic field B, x = shift of the electron beam on the screen, l = length of the field and L = distance between the centre of the field and the screen.

Milliken’s Oil Drop Method:

a) This method helps to determine the charge on the electron.

b) Let r be the density of oil, s is the density of the medium in which oil drop moves and the coefficient of viscosity of the medium, then the radius r of the drop is

Where v0 is the terminal velocity of the drop under the effect of gravity alone.

c) At the terminal velocity v0, the force due to viscosity becomes equal to the electric weight of the body.

d) The charge on oil drop is

Where v1 is the terminal velocity of the drop under the influence of electric field and gravity and E is the applied electric field.

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