Free Photons and the Particle Model of Light MCQs with Answers

• A. A & B
• B. B & C
• C. A & C
• D. A B & C

Explanation: X-ray quality means penetrating power and wavelength, which depend on the accelerating voltage and the target material.

• A. pair production
• B. Compton effect
• C. annihilation of matter
• D. X-rays production

Explanation: In the photoelectric effect, photons transfer energy to electrons and eject them from a metal.

• A. applied voltage
• B. frequency
• C. source
• D. all of the above

Explanation: The penetrating power of X-rays increases with photon energy, and photon energy is E = hf, so higher-frequency X-rays are more…

• A. of unknown nature
• B. high energy electrons
• C. high energy photons
• D. radio isotopes

Explanation: X-rays are electromagnetic radiation, so they consist of photons, not material electrons or radioactive isotopes.

• A. Photon theory of light
• B. Dual nature of light
• C. Wave nature of light
• D. Uncertain nature of light

Explanation: The Compton effect shows that light transfers momentum to electrons as if it consists of photons, supporting the photon or particle theory…

• A. 5.53 x 10^-36kg
• B. 0 kg.
• C. 2.46 x 10^-36kg
• D. 1.84 x 10^-44kg

Explanation: A photon has energy E = hc/λ, so its mass-equivalent is m = E/c^2 = h/(λc).

• A. The maximum kinetic energy of the photoelectrons increases
• B. The minimum kinetic energy of the photoelectrons decreases
• C. The minimum kinetic energy of the photoelectrons increases
• D. The average kinetic energy of the photoelectrons decreases

Explanation: Increasing wavelength lowers frequency because c = fλ, so the photon energy hf decreases.

• A. Becomes double
• B. Remains same
• C. Becomes half
• D. First increases then decrease because of the curvilinear graph

Explanation: For the same wavelength, each photon has the same energy hf, so doubling intensity only increases the number of photons and emitted…

• A. Increases because wavelength decreases
• B. Decreases because speed decreases
• C. Remains same
• D. Increases then decrease

Explanation: At a boundary, the photon frequency and hence its energy E = hf remain unchanged, although its speed and wavelength decrease in the denser…

• A. 103 photons of wavelength 2 pm (γ-rays)
• B. 102 photons of wavelength 1nm (x-rays)
• C. 106 photons of wavelength 50?m (infrared)
• D. 106 photons of wavelength 200nm (UV)

Explanation: Total energy is Nhc/λ. Taking hc = 1.986 x 10^-25 J m, option a gives (10^3)(1.986 x 10^-25 J m)/(2 x 10^-12 m) = 9.93 x 10^-11 J, which…

• A. A unit of energy
• B. A positively charged particle
• C. A quantum of electromagnetic radiation
• D. A unit of wavelength

Explanation: A photon is the smallest indivisible packet, or quantum, of electromagnetic radiation, with energy E = hf.

• A. The angle of scattering is 90°
• B. The angle of scattering is 60°
• C. The angle of scattering is 180°
• D. The angle of scattering is 0

Explanation: The Compton shift is Δλ = h(1 - cos θ)/(m_ec), so it is largest when cos θ = -1, which occurs at θ = 180°.

• A. 1/2 mvmax2=hf+Φ
• B. 1/2 mvmax2-hf = Φ
• C. 1/2 mvmax2=hf-Φ
• D. All of above are correct

Explanation: Einstein's photoelectric equation is hf = Φ + Kmax, so Kmax = 1/2 mvmax^2 = hf - Φ.

• A. infinite
• B. zero
• C. very small
• D. 1.67 x 10^-27 kg

Explanation: A photon has zero invariant or rest mass, although it carries energy E = hf and momentum p = E/c.

• A. the threshold frequency for the metal surface
• B. the intensity of incident light
• C. the frequency of incident light and work function of the metal surface
• D. all of the above

Explanation: The stopping potential satisfies eVs = hf - Φ = h(f - f0), so it depends on the incident frequency and the metal's work function, or…

• A. T.V waves
• B. Microwaves
• C. X-rays
• D. γ-rays

Explanation: Photon energy is E = hf, so radiation with the greatest frequency has the strongest, or most energetic, photons.

• A. Mass is not conserved
• B. Energy is not conserved
• C. Momentum is not conserved
• D. The chargee is not conserved

Explanation: A single photon cannot produce an electron-positron pair in empty space because energy and momentum cannot both be conserved by the…

• A. Net energy is conserved
• B. Net charge is conserved
• C. Net momentum is conserved
• D. All of the above

Explanation: In pair production, a high-energy photon becomes an electron and a positron near a heavy nucleus.

• A. waves
• B. particles
• C. photons
• D. it was not his discovery

Explanation: Einstein explained the photoelectric effect by treating light as discrete packets of energy called photons, with each photon carrying…

• A. Hertz
• B. Fresnel
• C. Einstein
• D. Plank

Explanation: Einstein explained the photoelectric effect by proposing that light consists of photons with energy E = hf, and that one photon transfers…