Free Dawn of Modern Physics MCQs with Answers

• A. Moving with speed of light
• B. At rest
• C. In accelerated form
• D. Moving with speed of sound

Explanation: A photon is a quantum of electromagnetic radiation and travels at 3.0 x 10^8 m/s in vacuum, the speed of light.

• A. Mosely
• B. Marley
• C. Arthur Holly Compton
• D. Stefan Boltzman

Explanation: Arthur Holly Compton explained the scattering of X-rays by electrons using the photon model and showed that the scattered wavelength…

• A. Two
• B. Three
• C. Four
• D. One

Explanation: When an electron and positron annihilate at rest, their rest energy is converted into two gamma-ray photons moving in opposite directions…

• A. Photon
• B. Meson
• C. Vector Boson
• D. Graviton

Explanation: The electromagnetic interaction is carried by photons, which are massless quantum particles of the electromagnetic field.

• A. Number of incident electron i.e. filament current
• B. The kinetic energy of the incident electron i.e. the potential difference through which they are accelerated
• C. The soft target which can easily emit electrons
• D. All of above are correct

Explanation: The maximum X-ray frequency follows h f_max = eV, so f_max = eV/h and is directly proportional to the accelerating potential difference…

• A. 6.2 x 10^-10m
• B. 9.1 x 10^-18m
• C. 3.11 x 10^-10m
• D. 4 x 10^-10m

Explanation: The minimum wavelength is λ_min = hc/eV = (6.63 x 10^-34 J s)(3.0 x 10^8 m/s)/(1.60 x 10^-19 C)(2000 V) = 6.2 x 10^-10 m.

• A. Reducing the pressure or cooling the target
• B. Increasing the temperature of the filament.
• C. Using a target element of higher atomic number
• D. Increasing the potential difference between the cathode and the target

Explanation: Since λ_min = hc/eV, increasing the potential difference V increases the electron energy and decreases the minimum X-ray wavelength.

• A. B-rays
• B. X-rays
• C. Far infrared
• D. Infrared

Explanation: Electrons accelerated through the high voltage in a television picture tube can strike the screen and produce bremsstrahlung X-rays…

• 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°.