NEET Dual Nature of Radiation and Matter PYQs & Practice Questions

10 free NEET Physics questions on Dual Nature of Radiation and Matter, starting with previous year questions (2016–2026). Tap “Show answer” to check each one. No login needed.

Topics: Photoelectric Effect - Work Function · Einstein's Photoelectric Equation · de Broglie Wavelength · Photon Properties · Davisson-Germer Experiment · Photoelectric Effect - Effect of Intensity and Frequency · De Broglie Wavelength Comparison · Photoelectric Effect Graphs · de Broglie Wavelength of a Falling Particle · Photon Wavelength for a Given Binding Energy · Electron Beam Striking a Metal Surface · Comparing de Broglie Wavelengths of Different Particles

Q1NEET 2026Photoelectric Effect - Current and Stopping Potential vs Time
A beam of light falls on a metal surface such that photo-electrons are generated. If power of the light source starts to decrease linearly with time t, then variation of the photocurrent I and magnitude of the stopping potential |V| with time is best represented by:
- A. I decreases linearly with t, and |V| also decreases linearly with t
- B. I stays constant (flat) with t, and |V| decreases linearly with t
- C. I stays constant (flat) with t, and |V| also stays constant (flat) with t
- D. I decreases linearly with t, and |V| stays constant (flat) with t
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Answer: C — I stays constant (flat) with t, and |V| also stays constant (flat) with t
Photocurrent is proportional to the intensity (power) of light, so as power decreases linearly with time, photocurrent I also decreases linearly. The stopping potential depends only on the frequency of light (not intensity), and since the frequency is unchanged, the stopping potential |V| remains constant over time.
Q2NEET 2026Photoelectric Effect - Threshold Wavelength and Stopping Potential
A ray of light with wavelength λ is incident on three different photo-electric cells namely 1, 2 and 3. The threshold wavelengths of these photo-electric cells are λ₁, λ₂, and λ₃ respectively and the magnitude of stopping potentials of these cells are V₁, V₂ and V₃ respectively. The relation between λ and threshold wavelengths are λ₁ < λ, λ₂ > λ and λ₃ >> λ. The correct option is:
- A. V₁ = 0, V₂ > V₃
- B. V₁ > V₂, V₃ = 0
- C. V₁ < V₂, V₃ = 0
- D. V₁ = 0, V₂ < V₃
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Answer: C — V₁ < V₂, V₃ = 0
Photoemission occurs only when the incident wavelength is less than the threshold wavelength (λ < λ_threshold), i.e., photon energy exceeds the work function. For cell 1: λ₁ < λ means the threshold wavelength is smaller than incident wavelength, so no photoemission occurs and V₁ = 0. For cell 2: λ₂ > λ, so photoemission occurs with some stopping potential V₂ > 0. For cell 3: λ₃ >> λ, so the incident photon energy far exceeds the work function, giving a much larger stopping potential V₃ >> V₂ > 0. Hence V₁ = 0 and V₂ < V₃.
Q3NEET 2026Momentum of Photon vs Electron
A photon and an electron, each of 20 eV energy, move in free space. The ratio of linear momentum of electron p_e to that of photon P_ph = p_e/P_ph is: (Take speed of light = 3×10⁸ ms⁻¹, charge of electron = −1.6×10⁻¹⁹ C and mass of electron = 9×10⁻³¹ kg)
- A. 1/250
- B. 225
- C. 275
- D. 2/450
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Answer: A — 1/250
Energy E = 20 eV = 20 × 1.6×10⁻¹⁹ = 3.2×10⁻¹⁸ J. Photon momentum: P_ph = E/c = 3.2×10⁻¹⁸/(3×10⁸) = 1.0667×10⁻²⁶ kg m/s. Electron momentum: p_e = √(2mE) = √(2×9×10⁻³¹×3.2×10⁻¹⁸) = √(5.76×10⁻⁴⁸) = 2.4×10⁻²⁴ kg m/s. Ratio p_e/P_ph = 2.4×10⁻²⁴/1.0667×10⁻²⁶ ≈ 225.
Q4NEET 2025De Broglie Wavelength Comparison
A photon and an electron (mass m) have the same energy E. The ratio (λphoton/λelectron) of their de Broglie wavelengths is : (c is the speed of light)
- A. √(E/2m)
- B. c√(2mE)
- C. c√(2m/E)
- D. (1/c)√(E/2m)
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Answer: B — c√(2mE)
λphoton = hc/E. λelectron = h/p = h/√(2mE). Ratio λph/λe = (hc/E)/(h/√(2mE)) = c√(2mE)/E = c√(2m/E).

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Q5NEET 2025Photoelectric Effect Graphs
Which of the following options represent the variation of photoelectric current with property of light shown on the x-axis? (A) current vs intensity - linear through origin; (B) current vs intensity - constant/flat; (C) current vs frequency - linear through origin; (D) current vs frequency - linear with a threshold intercept.
- A. A only
- B. A and C
- C. A and D
- D. B and D
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Answer: —
Photoelectric current is directly proportional to the intensity of incident light (graph A, straight line through origin), and is independent of frequency (above threshold) — so only option A is correct.
Q6NEET 2024Properties of Photon
If c is the velocity of light in free space, the correct statements about photon among the following are: A. The energy of a photon is E = hν. B. The velocity of a photon is c. C. The momentum of a photon, p = hν/c. D. In a photon-electron collision, both total energy and total momentum are conserved. E. Photon possesses positive charge. Choose the correct answer from the options given below:
- A. A, C and D only
- B. A, B, D and E only
- C. A and B only
- D. A, B, C and D only
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Answer: C — A and B only
A photon has energy E=hν (A, true), travels at velocity c (B, true), has momentum p=hν/c (C, true), and in photon-electron collisions both energy and momentum are conserved (D, true). A photon is chargeless/neutral, not positively charged (E, false). So A, B, C and D only.
Q7NEET 2024de Broglie Wavelength vs Kinetic Energy Graph
The graph which shows the variation of (1/λ²) and its kinetic energy E is (where λ is de Broglie wavelength of a free particle): [Four graph options showing different curve shapes of 1/λ² vs E]
- A. Concave down curve through origin (graph 1)
- B. Straight line through origin (graph 2)
- C. Concave up curve through origin (graph 3)
- D. Decreasing hyperbola-like curve (graph 4)
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Answer: A — Concave down curve through origin (graph 1)
λ = h/√(2mE), so λ² = h²/(2mE), giving E = h²/(2mλ²), i.e., E ∝ 1/λ². So 1/λ² is directly proportional to E, which is a straight line through the origin (graph 2).
Q8NEET 2023Photoelectric Effect - Work Function
The work functions of Caesium (Cs), Potassium (K) and Sodium (Na) are 2.14 eV, 2.30 eV and 2.75 eV respectively. If incident electromagnetic radiation has an incident energy of 2.20 eV, which of these photosensitive surfaces may emit photoelectrons?
- A. Both Na and K
- B. K only
- C. Na only
- D. Cs only
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Answer: C — Na only
Photoelectric emission occurs only when the incident photon energy exceeds the work function of the material. Since the incident energy (2.20 eV) is greater than Cs's work function (2.14 eV) but less than K's (2.30 eV) and Na's (2.75 eV), only Cs can emit photoelectrons.

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Q9NEET 2023X-ray Minimum Wavelength
The minimum wavelength of X-rays produced by an electron accelerated through a potential difference of V volts is proportional to:
- A. 1/V
- B. 1/√V
- C. V²
- D. √V
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Answer: —
The minimum wavelength of X-rays is given by λmin = hc/(eV), so λmin is proportional to 1/V.
Q10NEET 2022Photoelectric Effect Threshold Frequency
When two monochromatic lights of frequency ν and ν/2 are incident on a photoelectric metal, their stopping potential becomes Vs/2 and Vs respectively. The threshold frequency for this metal is:
- A. 3ν
- B. (2/3)ν
- C. (3/2)ν
- D. 2ν
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Answer: B — (2/3)ν
hν = w + eVs/2 ...(i); h(ν/2) = w + eVs ...(ii). Multiply (ii) by 2: hν = 2w + 2eVs. Subtract (i): hν - hν = (2w-w) + (2eVs - eVs/2) is reorganized as: from (i) and (ii), eliminating Vs gives 2hν - hν/2 = 2w - w ⟹ 3hν/2 = w = hνth ⟹ νth = 3ν/2.

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