Tamil Nadu Board of Secondary EducationHSC Science Class 12th

# Tamil Nadu Board Samacheer Kalvi solutions for Class 12th Physics Volume 1 and 2 Answers Guide chapter 8 - Dual Nature of Radiation and Matter [Latest edition]

## Chapter 8: Dual Nature of Radiation and Matter

Evaluation
Evaluation [Pages 135 - 138]

### Tamil Nadu Board Samacheer Kalvi solutions for Class 12th Physics Volume 1 and 2 Answers Guide Chapter 8 Dual Nature of Radiation and Matter Evaluation [Pages 135 - 138]

#### Multiple Choice Questions

Evaluation | Q I. 1. | Page 135

The wavelength λe of an electron and λp of a photon of same energy E are related by

• λ_"p" ∝ λ_"e"

• λ_"p" ∝ sqrt(λ_"e")

• λ_"p" ∝ 1/sqrt(λ_"e")

• λ_"p" ∝ λ_"e"^2

Evaluation | Q I. 2. | Page 135

In an electron microscope, the electrons are accelerated by a voltage of 14 kV. If the voltage is changed to 224 kV, then the de Broglie wavelength associated with the electrons would

• increase by 2 times

• decrease by 2 times

• decrease by 4 times

• increase by 4 times

Evaluation | Q I. 3. | Page 135

The wave associated with a moving particle of mass 3 × 10–6 g has the same wavelength as an electron moving with a velocity 6 × 106 ms–1. The velocity of the particle is

• 1.82 × 10–18 ms–1

• 9 × 10–2 ms–1

• 3 × 10–31 ms–1

• 1.82 × 10–15 ms–1

Evaluation | Q I. 4. | Page 135

When a metallic surface is illuminated with radiation of wavelength λ, the stopping potential is V. If the same surface is illuminated with radiation of wavelength 2λ, the stopping potential is "V"/4. The threshold wavelength for the metallic surface is

• 5/2λ

Evaluation | Q I. 5. | Page 135

If a light of wavelength 330 nm is incident on a metal with work function 3.55 eV, the electrons are emitted. Then the wavelength of the wave associated with the emitted electron is (Take h = 6.6 × 10–34 Js)

• < 2.75 × 10–9 m

• ≥ 2.75 × 10–9 m

• ≤ 2.75 × 10–12 m

• < 2.5 × 10–10 m

Evaluation | Q I. 6. | Page 135

A photoelectric surface is illuminated successively by monochromatic light of wavelength λ and λ/2. If the maximum kinetic energy of the emitted photoelectrons in the second case is 3 times that in the first case, the work function of the material is

• "hc"/λ

• (2"hc")/λ

• "hc"/(3λ)

• "hc"/(2λ)

Evaluation | Q I. 7. | Page 135

In photoelectric emission, a radiation whose frequency is 4 times threshold frequency of a certain metal is incident on the metal. Then the maximum possible velocity of the emitted electron will be

• sqrt(("hv"_0)/"m")

• sqrt((6"hv"_0)/"m")

• 2sqrt(("hv"_0)/"m")

• sqrt(("hv"_0)/(2"m"))

Evaluation | Q I. 8. | Page 135

Two radiations with photon energies 0.9 eV and 3.3 eV respectively are falling on a metallic surface successively. If the work function of the metal is 0.6 eV, then the ratio of maximum speeds of emitted electrons in the two cases will be

• 1 : 4

• 1 : 3

• 1 : 1

• 1 : 9

Evaluation | Q I. 9. | Page 136

A light source of wavelength 520 nm emits 1.04 × 1015 photons per second while the second source of 460 nm produces 1.38 × 1015 photons per second. Then the ratio of power of second source to that of first source is

• 1.00

• 1.02

• 1.5

• 0.98

Evaluation | Q I. 10. | Page 136

If the mean wavelength of light from sun is taken as 550 nm and its mean power as 3.8 × 1026 W, then the average number of photons received by the human eye per second from sunlight is of the order of

• 1045

• 1042

• 1054

• 1051

Evaluation | Q I. 11. | Page 136

The threshold wavelength for a metal surface whose photoelectric work function is 3.313 eV is __________.

• 4125 Å

• 3750 Å

• 6000 Å

• 2062.5 Å

Evaluation | Q I. 12. | Page 136

A light of wavelength 500 nm is incident on a sensitive metal plate of photoelectric work function 1.235 eV. The kinetic energy of the photoelectrons emitted is (Take h = 6.6 × 10–34 Js)

• 0.58 eV

• 2.48 eV

• 1.24 eV

• 1.16 eV

Evaluation | Q I. 13. | Page 136

Photons of wavelength λ are incident on a metal. The most energetic electrons ejected from the metal are bent into a circular arc of radius R by a perpendicular magnetic field having magnitude B. The work function of the metal is

• "hc"/λ - "m"_"e" + ("e"^2"B"^2"R"^2)/(2"m"_"e")

• "hc"/λ + 2"m"_"e" ["eBR"/(2"m"_"e")]^2

• "hc"/λ - "m"_"e""c"^2 - ("e"^2"B"^2"R"^2)/(2"m"_"e")

• "hc"/λ - 2"m"_"e" ["eBR"/(2"m"_"e")]^2

Evaluation | Q I. 14. | Page 136

The work functions for metals A, B and C are 1.92 eV, 2.0 eV and 5.0 eV respectively. The metal/metals which will emit photoelectrons for a radiation of wavelength 4100Å is/are

• A only

• both A and B

• all these metals

• none

Evaluation | Q I. 15. | Page 136

Emission of electrons by the absorption of heat energy is called ____________ emission.

• photoelectric

• field

• thermionic

• secondary

Evaluation | Q II. 1. | Page 136

Why do metals have a large number of free electrons?

Evaluation | Q II. 2. | Page 136

Define the work function of a metal. Give its unit.

Evaluation | Q II. 3. | Page 136

What is the photoelectric effect?

Evaluation | Q II. 4. | Page 136

How does photocurrent vary with the intensity of the incident light?

Evaluation | Q II. 5. | Page 136

Give the definition of intensity of light according to quantum concept and its unit.

Evaluation | Q II. 6. | Page 136

How will you define threshold frequency?

Evaluation | Q II. 7. | Page 137

What is a photocell?

Evaluation | Q II. 7. | Page 137

Mention the different types of photocells.

Evaluation | Q II. 8. | Page 137

Write the expression for the de Broglie wavelength associated with a charged particle of charge q and mass m, when it is accelerated through a potential V.

Evaluation | Q II. 9. | Page 137

State de Broglie hypothesis.

Evaluation | Q II. 10. | Page 137

Why we do not see the wave properties of a baseball?

Evaluation | Q II. 11. | Page 137

A proton and an electron have the same kinetic energy. Which one has a greater de Broglie wavelength? Justify.

Evaluation | Q II. 12. | Page 137

Write the relationship of de Broglie wavelength λ associated with a particle of mass m in terms of its kinetic energy K.

Evaluation | Q II. 13. | Page 137

An electron and an alpha particle have the same kinetic energy. How are the de Broglie wavelengths associated with them related?

Evaluation | Q II. 14. | Page 137

Define stopping potential.

Evaluation | Q II. 15. | Page 137

What is a surface barrier?

Evaluation | Q II. 16. | Page 137

Mention the two features of x-ray spectra, not explained by classical electromagnetic theory.

Evaluation | Q II. 17. | Page 137

What is Bremsstrahlung?

Evaluation | Q III. 1. | Page 137

What do you mean by electron emission? Explain briefly various methods of electron emission.

Evaluation | Q III. 2. | Page 137

Briefly discuss the observations of Hertz, Hallwachs and Lenard.

Evaluation | Q III. 3. | Page 137

Explain the effect of potential difference on photoelectric current.

Evaluation | Q III. 4. | Page 137

Explain how frequency of incident light varies with stopping potential.

Evaluation | Q III. 5. | Page 137

List out the laws of photoelectric effect.

Evaluation | Q III. 6. | Page 137

Explain why photoelectric effect cannot be explained on the basis of wave nature of light.

Evaluation | Q III. 7. | Page 137

Explain the quantum concept of light.

Evaluation | Q III. 8. | Page 137

Obtain Einstein’s photoelectric equation with the necessary explanation.

Evaluation | Q III. 9. | Page 137

Explain experimentally observed facts of the photoelectric effect with the help of Einstein’s explanation.

Evaluation | Q III. 10. | Page 137

Give the construction and working of photo emissive cell.

Evaluation | Q III. 11. | Page 137

Derive an expression for de Broglie wavelength of electrons.

Evaluation | Q III. 12. | Page 137

Briefly explain the principle and working of electron microscope.

Evaluation | Q III. 13. | Page 137

Describe briefly Davisson – Germer experiment which demonstrated the wave nature of electrons.

Evaluation | Q III. 14. | Page 137

List out the characteristics of photons.

Evaluation | Q III. 15. | Page 137

Give the applications photocell.

Evaluation | Q III. 16. | Page 137

How do we obtain characteristic x-ray spectra?

#### Numerical problems

Evaluation | Q IV. 1. | Page 137

How many photons per second emanate from a 50 mW laser of 640 nm?

Evaluation | Q IV. 2. | Page 137

Calculate the maximum kinetic energy and maximum velocity of the photoelectrons emitted when the stopping potential is 81 V for the photoelectric emission experiment.

Evaluation | Q IV. 3. | Page 137

Calculate the energies of the photons associated with the following radiation:

1. violet light of 413 nm
2. X-rays of 0.1 nm
3. radio waves of 10 m
Evaluation | Q IV. 4. | Page 138

A 150 W lamp emits light of the mean wavelength of 5500 Å. If the efficiency is 12%, find out the number of photons emitted by the lamp in one second.

Evaluation | Q IV. 5. | Page 138

How many photons of frequency 1014 Hz will make up 19.86 J of energy?

Evaluation | Q IV. 6. | Page 138

What should be the velocity of the electron so that its momentum equals that of 4000 Å wavelength photon.

Evaluation | Q IV. 7. | Page 138

When a light of frequency 9 × 1014 Hz is incident on a metal surface, photoelectrons are emitted with a maximum speed of 8 × 105 ms−1. Determine the threshold frequency of the surface.

Evaluation | Q IV. 8. | Page 138

When a 6000 Å light falls on the cathode of a photo cell, photoemission takes place. If a potential of 0.8 V is required to stop emission of electron, then determine the

1. frequency of the light
2. energy of the incident photon
3. work function of the cathode material
4. threshold frequency and
5. net energy of the electron after it leaves the surface.
Evaluation | Q IV. 9. | Page 138

A 3310 Å photon liberates an electron from a material with energy 3 × 10−19 J while another 5000 Å photon ejects an electron with energy 0.972 × 10−19 J from the same material. Determine the value of Planck’s constant and the threshold wavelength of the material.

Evaluation | Q IV. 10. | Page 138

At the given point of time, the earth receives energy from the sun at 4 cal cm–2 min–1. Determine the number of photons received on the surface of the Earth per cm2 per minute. (Given: Mean wavelength of sunlight = 5500 Å)

Evaluation | Q IV. 11. | Page 138

UV light of wavelength 1800 Å is incident on a lithium surface whose threshold wavelength is 4965 Å. Determine the maximum energy of the electron emitted.

Evaluation | Q IV. 12. | Page 138

Calculate the de Broglie wavelength of a proton whose kinetic energy is equal to 81.9 × 10–15 J.
(Given: mass of proton is 1836 times that of electron).

Evaluation | Q IV. 13. | Page 138

A deuteron and an alpha particle are accelerated with the same potential. Which one of the two has

1. greater value of de Broglie wavelength associated with it and
2. less kinetic energy?

Explain.

Evaluation | Q IV. 14. | Page 138

An electron is accelerated through a potential difference of 81 V. What is the de Broglie wavelength associated with it? To which part of the electromagnetic spectrum does this wavelength correspond?

Evaluation | Q IV. 15. | Page 138

The ratio between the de Broglie wavelength associated with proton accelerated through a potential of 512 V and that of alpha particle accelerated through a potential of X volts is found to be one. Find the value of X.

Evaluation

## Tamil Nadu Board Samacheer Kalvi solutions for Class 12th Physics Volume 1 and 2 Answers Guide chapter 8 - Dual Nature of Radiation and Matter

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Concepts covered in Class 12th Physics Volume 1 and 2 Answers Guide chapter 8 Dual Nature of Radiation and Matter are Electron Emission, Photo Electric Effect, Matter Waves.

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