Willer Academy

Concept Check Test: Dual Nature of Light and Matter

Instructions

• This test contains 35 questions - 25 Multiple Choice Questions and 10 Assertion-Reasoning Questions
• Each question carries 1 mark
• There is no negative marking
• Select the most appropriate answer for each question
• Click "Submit Test" when you are finished to see your score
• Use "Show Answers" button to review correct answers with explanations

Time: 60 minutes

M.M.: 35

Subject: Physics

Question 1 MCQ

Which phenomenon first demonstrated the particle nature of light?

Diffraction Interference Photoelectric effect Polarization

Question 2 MCQ

What is the rest mass of a photon?

0 ∞ 1.67 × 10⁻²⁷ kg 9.1 × 10⁻³¹ kg

Question 3 MCQ

If the frequency of incident light in a photoelectric experiment is doubled, the maximum kinetic energy of the photoelectrons becomes:

Doubled More than doubled Less than doubled Unchanged

Question 4 MCQ

The de Broglie wavelength of an electron accelerated by a potential of V volts is given by:

λ = 1.227/√V nm λ = 12.27/√V Å λ = 12.27/√V nm Both (a) and (b)

Question 5 MCQ

The work function of a material depends on:

Frequency of incident light Intensity of incident light The nature of the material The stopping potential

Question 6 MCQ

A photon and an electron have the same de Broglie wavelength. Which one has higher kinetic energy?

Electron Photon Both have the same Information insufficient

Question 7 MCQ

In the photoelectric effect, the number of photoelectrons emitted is proportional to:

Frequency of incident light Intensity of incident light Work function of the material Stopping potential

Question 8 MCQ

The de Broglie hypothesis is applicable to:

Electrons only Protons only Photons only All material particles

Question 9 MCQ

The stopping potential in photoelectric effect depends on:

Intensity of incident light Frequency of incident light Both intensity and frequency Neither intensity nor frequency

Question 10 MCQ

Which of the following has the longest de Broglie wavelength, if they have the same kinetic energy?

Electron Proton Alpha particle Neutron

Question 11 MCQ

The photoelectric effect can be explained by:

Wave theory of light Quantum theory of light Corpuscular theory of light Electromagnetic theory of light

Question 12 MCQ

The momentum of a photon of wavelength λ is:

hλ h/λ hλ/c h/λc

Question 13 MCQ

The threshold frequency for a photosensitive metal is ν₀. When light of frequency 2ν₀ is incident on it, the maximum velocity of photoelectrons is v₀. What will be the maximum velocity of photoelectrons when light of frequency 5ν₀ is incident on it?

2v₀ √2 v₀ 4v₀ 2√2 v₀

Question 14 MCQ

Which of the following statements is true for both photons and electrons?

They both can be deflected by electric and magnetic fields They both exhibit wave-particle duality They both have rest mass They both travel at the speed of light

Question 15 MCQ

In Davisson and Germer experiment, the intensity of scattered electrons is maximum when:

Angle of scattering is 0° Angle of scattering is 90° Angle of scattering is 180° At a specific angle that satisfies Bragg's law

Question 16 MCQ

The energy of a photon is 3 eV. What is the wavelength of the photon? (h = 4.14 × 10⁻¹⁵ eV·s, c = 3 × 10⁸ m/s)

4133 Å 4133 nm 2066 Å 2066 nm

Question 17 MCQ

The de Broglie wavelength of a particle of mass m and charge Q accelerated by a potential V is:

λ = h/√(2mQV) λ = h/√(2mV) λ = h/√(2mQ) λ = h/√(2QV)

Question 18 MCQ

The ratio of de Broglie wavelengths of a proton and an α-particle accelerated through the same potential is:

1:1 1:2 2:1 2√2:1

Question 19 MCQ

In photoelectric effect, the graph between stopping potential and frequency of incident light is:

A straight line with positive intercept on frequency axis A straight line with negative intercept on frequency axis A parabola A hyperbola

Question 20 MCQ

The photoelectric current increases with increase in:

Frequency of incident light Wavelength of incident light Intensity of incident light Work function of the material

Question 21 MCQ

Which of the following has the smallest de Broglie wavelength, if they have the same velocity?

Electron Proton Alpha particle Neutron

Question 22 MCQ

The kinetic energy of an electron is 5 eV. What is the de Broglie wavelength of this electron? (Given: h = 6.63 × 10⁻³⁴ J·s, m = 9.1 × 10⁻³¹ kg, 1 eV = 1.6 × 10⁻¹⁹ J)

5.47 Å 10.9 Å 2.7 Å 1.09 Å

Question 23 MCQ

The photoelectric effect is not observed below the threshold frequency because:

The energy of photons is insufficient to eject electrons The intensity of light is too low The light is not polarized The material has too high work function

Question 24 MCQ

Which of the following graphs represents the variation of photoelectric current with intensity of incident light?

Linear with positive slope Linear with negative slope Parabolic Hyperbolic

Question 25 MCQ

The de Broglie wavelength of a neutron at 27°C is λ. What will be its wavelength at 927°C?

λ/2 λ/4 2λ 4λ

Question 26 Assertion-Reason

Assertion (A): Photoelectric effect demonstrates the particle nature of light.

Reason (R): The kinetic energy of photoelectrons depends on the intensity of incident light.

Both A and R are true and R is the correct explanation of A Both A and R are true but R is NOT the correct explanation of A A is true but R is false A is false but R is true

Question 27 Assertion-Reason

Assertion (A): Davisson-Germer experiment confirms the wave nature of electrons.

Reason (R): Electrons show diffraction pattern when scattered by crystals.

Both A and R are true and R is the correct explanation of A Both A and R are true but R is NOT the correct explanation of A A is true but R is false A is false but R is true

Question 28 Assertion-Reason

Assertion (A): Light can behave as both wave and particle.

Reason (R): Light shows interference and diffraction (wave nature) and photoelectric effect (particle nature).

Both A and R are true and R is the correct explanation of A Both A and R are true but R is NOT the correct explanation of A A is true but R is false A is false but R is true

Question 29 Assertion-Reason

Assertion (A): The photoelectric effect cannot be explained by wave theory.

Reason (R): Wave theory predicts that kinetic energy should increase with intensity, but experimentally it depends on frequency.

Both A and R are true and R is the correct explanation of A Both A and R are true but R is NOT the correct explanation of A A is true but R is false A is false but R is true

Question 30 Assertion-Reason

Assertion (A): De Broglie wavelength is significant only for microscopic particles.

Reason (R): De Broglie wavelength is inversely proportional to mass.

Both A and R are true and R is the correct explanation of A Both A and R are true but R is NOT the correct explanation of A A is true but R is false A is false but R is true

Question 31 Assertion-Reason

Assertion (A): Photons exert pressure on surfaces on which they strike.

Reason (R): Photons have momentum as well as energy.

Both A and R are true and R is the correct explanation of A Both A and R are true but R is NOT the correct explanation of A A is true but R is false A is false but R is true

Question 32 Assertion-Reason

Assertion (A): The maximum kinetic energy of photoelectrons is independent of intensity of incident light.

Reason (R): The photoelectric current is proportional to the intensity of incident light.

Both A and R are true and R is the correct explanation of A Both A and R are true but R is NOT the correct explanation of A A is true but R is false A is false but R is true

Question 33 Assertion-Reason

Assertion (A): Electrons cannot be accelerated to velocities greater than that of light.

Reason (R): The mass of electron increases with velocity.

Both A and R are true and R is the correct explanation of A Both A and R are true but R is NOT the correct explanation of A A is true but R is false A is false but R is true

Question 34 Assertion-Reason

Assertion (A): X-rays cannot eject electrons from metals.

Reason (R): The energy of X-ray photons is too high.

Both A and R are true and R is the correct explanation of A Both A and R are true but R is NOT the correct explanation of A A is true but R is false A is false but R is true

Question 35 Assertion-Reason

Assertion (A): In photoelectric effect, the stopping potential depends on the frequency of incident light.

Reason (R): The maximum kinetic energy of photoelectrons depends on the frequency of incident light.

Both A and R are true and R is the correct explanation of A Both A and R are true but R is NOT the correct explanation of A A is true but R is false A is false but R is true

Test Results

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Answers and Explanations

Question 1: Which phenomenon first demonstrated the particle nature of light?
Answer: Photoelectric effect

Explanation: The photoelectric effect, explained by Einstein using photon concept, provided the first evidence of light's particle nature.

Question 2: What is the rest mass of a photon?
Answer: 0

Explanation: Photons are massless particles that always travel at the speed of light in vacuum.

Question 3: If the frequency of incident light in a photoelectric experiment is doubled, the maximum kinetic energy of the photoelectrons becomes:
Answer: More than doubled

Explanation: K.E._max = hν - φ. Doubling frequency more than doubles K.E. as work function φ remains constant.

Question 4: The de Broglie wavelength of an electron accelerated by a potential of V volts is given by:
Answer: Both (a) and (b)

Explanation: λ = h/√(2meV) which equals 1.227/√V nm or 12.27/√V Å. Both represent the same value.

Question 5: The work function of a material depends on:
Answer: The nature of the material

Explanation: Work function is an intrinsic property of the material and depends on its electronic structure.

Question 6: A photon and an electron have the same de Broglie wavelength. Which one has higher kinetic energy?
Answer: Photon

Explanation: For the same de Broglie wavelength, the photon has higher energy as E = hc/λ, while electron energy is h²/(2mλ²).

Question 7: In the photoelectric effect, the number of photoelectrons emitted is proportional to:
Answer: Intensity of incident light

Explanation: Higher intensity means more photons, which results in more photoelectrons emitted.

Question 8: The de Broglie hypothesis is applicable to:
Answer: All material particles

Explanation: De Broglie proposed that all moving particles have wave characteristics, not just electrons.

Question 9: The stopping potential in photoelectric effect depends on:
Answer: Frequency of incident light

Explanation: Stopping potential is related to maximum kinetic energy, which depends on frequency (K.E._max = hν - φ).

Question 10: Which of the following has the longest de Broglie wavelength, if they have the same kinetic energy?
Answer: Electron

Explanation: λ = h/√(2mK). For same K, λ is inversely proportional to √m. Electron has smallest mass, so longest wavelength.

Question 11: The photoelectric effect can be explained by:
Answer: Quantum theory of light

Explanation: Quantum theory explains photoelectric effect using photon concept, while wave theory fails to explain it.

Question 12: The momentum of a photon of wavelength λ is:
Answer: h/λ

Explanation: According to de Broglie relation, p = h/λ for photons and all particles.

Question 13: The threshold frequency for a photosensitive metal is ν₀. When light of frequency 2ν₀ is incident on it, the maximum velocity of photoelectrons is v₀. What will be the maximum velocity of photoelectrons when light of frequency 5ν₀ is incident on it?
Answer: 2v₀

Explanation: K.E.₁ = h(2ν₀) - hν₀ = hν₀ = ½mv₀². K.E.₂ = h(5ν₀) - hν₀ = 4hν₀ = ½mv². So v = 2v₀.

Question 14: Which of the following statements is true for both photons and electrons?
Answer: They both exhibit wave-particle duality

Explanation: Both photons and electrons show both wave and particle properties.

Question 15: In Davisson and Germer experiment, the intensity of scattered electrons is maximum when:
Answer: At a specific angle that satisfies Bragg's law

Explanation: The maximum intensity occurs when the angle satisfies Bragg's condition for crystal diffraction, confirming wave nature.

Question 16: The energy of a photon is 3 eV. What is the wavelength of the photon? (h = 4.14 × 10⁻¹⁵ eV·s, c = 3 × 10⁸ m/s)
Answer: 4133 Å

Explanation: λ = hc/E = (12400 eV·Å)/(3 eV) ≈ 4133 Å.

Question 17: The de Broglie wavelength of a particle of mass m and charge Q accelerated by a potential V is:
Answer: λ = h/√(2mQV)

Explanation: Kinetic energy gained = QV = p²/2m, so p = √(2mQV) and λ = h/p = h/√(2mQV).

Question 18: The ratio of de Broglie wavelengths of a proton and an α-particle accelerated through the same potential is:
Answer: 2√2:1

Explanation: λ = h/√(2mQV). For proton: m, Q. For α-particle: 4m, 2Q. So λ_p/λ_α = √( (4m×2Q) / (m×Q) ) = √8 = 2√2.

Question 19: In photoelectric effect, the graph between stopping potential and frequency of incident light is:
Answer: A straight line with negative intercept on frequency axis

Explanation: The equation is V_s = (h/e)ν - φ/e, which is a straight line with slope h/e and negative intercept on ν-axis.

Question 20: The photoelectric current increases with increase in:
Answer: Intensity of incident light

Explanation: Higher intensity means more photons, which results in more photoelectrons and higher current.

Question 21: Which of the following has the smallest de Broglie wavelength, if they have the same velocity?
Answer: Alpha particle

Explanation: λ = h/mv. For same v, λ is inversely proportional to m. Alpha particle has largest mass, so smallest wavelength.

Question 22: The kinetic energy of an electron is 5 eV. What is the de Broglie wavelength of this electron? (Given: h = 6.63 × 10⁻³⁴ J·s, m = 9.1 × 10⁻³¹ kg, 1 eV = 1.6 × 10⁻¹⁹ J)
Answer: 5.47 Å

Explanation: λ = h/√(2mK) = 6.63×10⁻³⁴/√(2×9.1×10⁻³¹×5×1.6×10⁻¹⁹) ≈ 5.47×10⁻¹⁰ m = 5.47 Å.

Question 23: The photoelectric effect is not observed below the threshold frequency because:
Answer: The energy of photons is insufficient to eject electrons

Explanation: Below threshold frequency, photon energy hν < φ (work function), so electrons cannot be ejected.

Question 24: Which of the following graphs represents the variation of photoelectric current with intensity of incident light?
Answer: Linear with positive slope

Explanation: Photoelectric current is directly proportional to intensity of light, so the graph is a straight line with positive slope.

Question 25: The de Broglie wavelength of a neutron at 27°C is λ. What will be its wavelength at 927°C?
Answer: λ/2

Explanation: λ = h/√(2mkT). Temperature ratio: (27+273):(927+273) = 300:1200 = 1:4. So λ₂/λ₁ = √(T₁/T₂) = √(1/4) = 1/2.

Question 26: Assertion-Reason Question
Answer: A is true but R is false

Explanation: While photoelectric effect does demonstrate particle nature (A is true), the kinetic energy depends on frequency, not intensity (R is false).

Question 27: Assertion-Reason Question
Answer: Both A and R are true and R is the correct explanation of A

Explanation: Davisson-Germer experiment confirmed wave nature of electrons (A is true) through observation of diffraction patterns (R is true and explains A).

Question 28: Assertion-Reason Question
Answer: Both A and R are true and R is the correct explanation of A

Explanation: Light exhibits dual nature (A is true) as shown by interference/diffraction (wave) and photoelectric effect (particle) (R is true and explains A).

Question 29: Assertion-Reason Question
Answer: Both A and R are true and R is the correct explanation of A

Explanation: Wave theory cannot explain photoelectric effect (A is true) because it predicts wrong dependence on intensity rather than frequency (R is true and explains A).

Question 30: Assertion-Reason Question
Answer: Both A and R are true and R is the correct explanation of A

Explanation: De Broglie wavelength is significant only for microscopic particles (A is true) because λ = h/mv, so for large m, λ becomes very small (R is true and explains A).

Question 31: Assertion-Reason Question
Answer: Both A and R are true and R is the correct explanation of A

Explanation: Photons exert pressure (A is true) because they have momentum p = h/λ (R is true and explains A).

Question 32: Assertion-Reason Question
Answer: Both A and R are true but R is NOT the correct explanation of A

Explanation: Maximum K.E. is independent of intensity (A is true) and current is proportional to intensity (R is true), but R does not explain A as they are separate facts.

Question 33: Assertion-Reason Question
Answer: Both A and R are true and R is the correct explanation of A

Explanation: Electrons cannot exceed light speed (A is true) because their mass increases with velocity approaching infinity at light speed (R is true and explains A).

Question 34: Assertion-Reason Question
Answer: A is false but R is true

Explanation: X-rays can eject electrons (A is false) and they do have high energy (R is true). In fact, X-rays can cause photoelectric effect.

Question 35: Assertion-Reason Question
Answer: Both A and R are true and R is the correct explanation of A

Explanation: Stopping potential depends on frequency (A is true) because maximum K.E. depends on frequency (R is true and explains A).

Willer Academy Physics Test • Dual Nature of Light and Matter • © 2023