Establish the Einstein's equation 1 2 m v m a x 2 = h v - v 0 and explain the laws of photoelectric effect on its basis.

Einstein explained photoelectric effect on the basis of quantum theory. The main points are 1. Light is propagated in the form of bundles of energy.called quanta having energy given by the Plank's relation. E = hν Where ν = frequency and h = Plank's constant 2 The photoelectric effect is due to collision of a photon of incident light and a bound electron of the metallic cathode. The interaction between the incident quanta and the electron of the metal is instantaneous ( ≃ 10 - 9 s e c . ) (3). The interacting photon transfers its whole energy to a single electron. (4) The energy of photon goes in two parts: a part of energy is used in ejecting the electron from the metal surface(i.e., in overcoming work function) and the remaining part appears in the form of kinetic energy of the same electron If ν be the frequency of incident light, the energy of photon h ν If ϕ 0 be the work function, The maximum KE of the emitted electrons is K max = 1 2 mv 2 = hν - ϕ 0 If the incident photon is of the threshold frequency ( ν 0 ), just sufficient to eject the electron from the metal, then ϕ 0 = hν 0 Hence, the equation becomes 1 2 m v m a x 2 = hν - hv 0 = h ν - ν 0 Explanation of Laws of Photoelectric emission (1) Since one incident photon can eject one photoelectron from the metal, number of photoelectron emitted (photo current) will be perorational to the number of incident photons (intensity of incident radiations) (2) If the frequency(energy) of the incident radiation is less than hν 0 (threshold frequency), no photoemission is possible. (3) For the radiations having energy greater than the threshold value, The maximum kinetic energy of the emitted electrons is proportional to the frequency of the incident radiation, as it is indicated by the formula KE ∝ ν . The kinetic energy of the emitted radiation is independent of the intensity of incident radiation. (iv) The effect is due to the elastic collisions between the incident photons and the electrons of the metal. The absorption of energy by the electrons is a single event involves transfer of energy instantaneously This explains the laws of photo electric effect.

E M B I B E

ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 1

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IMPORTANT

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Explain work function and threshold frequency in photoelectric emission. Give Einstein’s equation for photoelectric emission. What do the symbols stand for?

Important Questions on Photoelectric Effect

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12th ICSE

IMPORTANT

ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 2

Draw a graph between the frequency of light used for photoelectric effect and the maximum kinetic energy of the emitted photoelectrons. Explain: What does the slope of the graph represent?

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IMPORTANT

ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 2

Draw a graph between the frequency of light used for photoelectric effect and the maximum kinetic energy of the emitted photoelectrons. Explain: How is the work function of the metal surface obtained by the graph?

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IMPORTANT

ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 2

Draw a graph between the frequency of light used for photoelectric effect and the maximum kinetic energy of the emitted photoelectrons. Explain: What will be the effect on the nature of the graph, if the intensity of the incident light be doubled, or metal of lower work function be taken?

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ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 3

State the dependence of work function on the kinetic energy of the electrons emitted in a photocell. If the intensity of incident radiation is doubled,what changes occur in the stopping potential, kinetic energy of the photoelectrons and the photoelectric current?

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IMPORTANT

ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 4

Establish the Einstein's equation $\frac{1}{2} m v_{m a x}^{2} = h (v - v_{0})$ and explain the laws of photoelectric effect on its basis.

HARD

12th ICSE

IMPORTANT

ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 5

Plot a labelled graph of

(V_{0})

, where

V_{0}

is the stopping potential of photoelectrons versus frequency

v

of incident radiation. How will you use this graph to determine the value of Planck's constant? Explain.

HARD

12th ICSE

IMPORTANT

ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 1

State the phenomenon of photoelectric effect and explain the dependence of photocurrent and stopping potential on intensity and frequency.

HARD

12th ICSE

IMPORTANT

ISC Physics Class 12, Part-2>Chapter 10 - Photoelectric Effect>QUESTIONS>Q 2

Define threshold frequency, work function and cut-off potential. Draw a graph between maximum kinetic energy against frequency of light falling on a metal surface.

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