CBSE Class 12 · 2013 · Modern PhysicsShort Answer

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Write Einstein's photoelectric equation and point out any two characteristic properties of photons on which this equation is based. Briefly explain the three observed features which can be explained by this equation.

Answer: $K_{ma x} = h ν - ϕ_{0}$ ; explains threshold, $K_{ma x} \propto ν$ , current $\propto$ intensity.

Solution

Einstein's equation:

K_{ma x} = h ν - ϕ_{0}

.
Properties of photons used: (i) a photon carries a definite energy

E = h ν

(particle nature of light); (ii) one photon is absorbed completely by one electron in a single interaction.
Three observed features explained:
(1) No emission below a threshold frequency

ν_{0} = ϕ_{0} / h

(for

ν < ν_{0}

K_{ma x}

would be negative).
(2)

K_{ma x}

increases linearly with frequency and is independent of intensity.
(3) The number of photoelectrons (saturation current) is proportional to the intensity, and emission is instantaneous.

K_{ma x} = h ν - ϕ_{0}

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CBSE Class 12 · 2013 · Modern PhysicsShort Answer

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