CBSE Class 12 · 2016 · All India · Modern PhysicsShort Answer

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State two important properties of the photon which are used to write Einstein's photoelectric equation. Define
(i) stopping potential and
(ii) threshold frequency, using Einstein's equation and drawing the necessary plot between relevant quantities.

Answer: Photon: $E = h ν$ , one-photon-one-electron. $e V_{0} = K_{ma x}$ ; $ν_{0} = ϕ_{0} / h$ .

Solution

Two properties of a photon: (i) a photon of light of frequency

ν

carries energy

E = h ν

; (ii) it has zero rest mass and interacts with a single electron, transferring all its energy in one act.
Einstein's equation:

e V_{0} = K_{ma x} = h ν - ϕ_{0}

.
(i) Stopping potential

V_{0}

: retarding potential at which the photocurrent is zero;

e V_{0} = K_{ma x}

.
(ii) Threshold frequency

ν_{0} = ϕ_{0} / h

: the frequency below which

K_{ma x} \leq 0

, so no emission occurs.
The plot of

V_{0}

versus

ν

is a straight line of slope

h / e

cutting the frequency axis at

ν_{0}

(see figure).

e V_{0} = h ν - ϕ_{0}, ν_{0} = ϕ_{0} / h

CBSE Class 12 Board · 2016 · All India · Subjective

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CBSE Class 12 · 2016 · All India · Modern PhysicsShort Answer

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