Establish Einstein's relation 1 2 mu 2 = hv - hv 0 with respect to photoelectric emission.

The phenomenon of emission of electrons from a metal surface, when electromagnetic radiations of sufficiently high frequency are incident on it, is called the photoelectric effect. Einstein explained the photoelectric effect based on Planck's quantum theory according to which light radiation travels in the form of discrete photons. The energy of each photon is hv , where h is Planck's constant and v is the frequency of light. The main points of Einstein’s theory of the photoelectric effect are: The interaction between two particles results in photoelectric emission– one a photon of incident radiation and the other an electron of photosensitive metal. The free electrons are bound within the metal due to restraining forces on the surface. The minimum energy required to liberate an electron from the metal surface is called the work function W 0 of the metal. Each photon interacts with one electron. The energy hv of the incident photon is used up in two parts: A part of the energy of the photon is used in liberating the electron from the metal surface, which is equal to the work function W 0 of the metal, and The remaining energy of the photon is used in impairing kinetic energy to the ejected electron. Very few < 1 0 0 photons, whose energies are greater than W 0 , capable of ejecting the photons. By law of the conservation of energy, Energy of the incident photon = Maximum K . E . of photon + Work function hv = 1 2 mv 2 max + W 0 ∴ K max = 1 2 mv 2 max = hv - W 0 . . . . . . . ( 1 ) If the incident photon is threshold frequency v 0 , then its energy hv 0 is just sufficient to free the electron from the metal surface and does not give it any kinetic energy. So hv 0 = W 0 . Hence K max = 1 2 mv 2 max = hv - hv 0 = h v - v 0 . . . . . . ( 2 ) Equations (1) and (2) are called Einstein’s photoelectric equations.A

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Which of the following phenomena can be explained only on the basis of quantum theory of light ?

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Important Questions on Dual Nature of Matter and Radiation

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Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

Which one of the following particle is a boson?

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Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

Establish Einstein's relation

\frac{1}{2} {mu}^{2} = hv - {hv}_{0}

with respect to photoelectric emission.

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Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

Write any two applications of photoelectric cell.

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Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

Photoelectric effect represents:

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Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

If the work function for the photoelectron emission of a metal is

3.75 eV

, then the threshold wave length of the radiation needed for the ejection of the electron is approximately

EASY

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

Find the energy

(in eV)

of an X-ray photon of wavelength

λ = 1 \overset{o}{A}

EASY

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

Charge on an electron is

- 1.6 \times 10^{z}

coulomb. The value of

z

is _____.

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Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

Photoelectrons are emitted from a given metal surface when it is illuminated by two beams

P

and

Q

of light, both having the same frequency. The saturation value of the photocurrent produced by

P

has a magnitude which is four times that produced by

Q .

The ratio of the electric field strength in beam

P

to that in

Q

HARD

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

Why is wave theory of electromagnetic radiation is not able to explain photo electric effect? How does photon picture resolve this problem?

EASY

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

Define threshold frequency.

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Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

What is "Photoelectric effect"?

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Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

When photon of energy

4.0 eV

strikes the surface of a metal

A

, the elected photoelectrons have maximum kinetic energy

T_{A} eV

and de-Broglie wavelength

λ_{A}

. The maximum kinetic energy of photoelectron liberated from another metal

B

by photon of energy

4.50 eV

T_{B} = (T_{A} - 1.50) eV

. If the de-Broglie wavelength of these photoelectrons

λ_{B} = 2 λ_{A}

, then choose the correct statement(s).

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Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

Light of frequency

8.41 \times 10^{14} H z

is incident on a metal surface. Electrons with a maximum speed of

7.5 \times 10^{5} m s^{- 1}

are ejected from the surface. Calculate the threshold frequency for photo emission of electrons. Also find the work function of the metal in electron volt (eV). Given, Planck's constant

h = 6.625 \times 10^{- 34} J s^{- 1}

and mass of the electron

m = 9.1 \times 10^{- 31} K g .

EASY

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

The force carrier in the case of

EM

waves is

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Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

What is meant by the dual nature of light?

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Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

The typical electric field required for electrons to be emitted from surfaces of metals by the "field emission" process is about

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Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

In a photoelectric effect experiment, a point source of light of power

3.2 mW

emits photons each of which has

5 eV

energy. The source is located at a distance of

0.8 m

from the centre of a stationary metal disk having a work function of

3 eV .

The metal disk has a radius of

8 \times 10^{- 3} m .

Assuming that one photoelectron is emitted for every

10^{6}

photons striking the surface of the disk, how many photoelectrons are emitted every second?

EASY

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

A laser produces monochromatic light of wavelength

530.4 nm

. The power emitted is

3.0 mW

. The number of photons emitted per second on an average is

(h = 6.63 \times 10^{- 34} Js, c = 3 \times 10^{8} {ms}^{- 1})

EASY

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

State Heisenberg's Uncertainty principle.

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Physics>Modern Physics>Dual Nature of Matter and Radiation>Photon Theory of Light

In the line spectra of hydrogen atom, difference between the largest and the shortest wavelengths of the Lyman series is

305 \overset{\circ}{A}

. The corresponding difference for the Paschan series in

\overset{\circ}{A}

is:________. (nearest integer)

Which of the following phenomena can be explained only on the basis of quantum theory of light ?

Important Questions on Dual Nature of Matter and Radiation

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