Free Dawn of Modern Physics MCQs with Answers

• A. Red
• B. Blue
• C. Yellow
• D. Orange

Explanation: The correct answer is Option B: Blue. When heating iron, the color blue signifies the highest temperature.

• A. Mass and velocity
• B. Position and mass
• C. Mass and momentum
• D. Position and momentum

Explanation: The Heisenberg uncertainty principle is a cornerstone of quantum mechanics, stating that there is a fundamental limit to the precision…

• A. becomes zero.
• B. remains the same.
• C. shifts to the longer wavelength.
• D. shifts to the shorter wavelength.

Explanation: When the temperature of a black body is lowered, according to Wien's displacement law, the wavelength associated with the maximum…

• A. It is the most efficient radiator.
• B. It is a perfect absorber of radiation.
• C. Its absorption power is equal to one.
• D. It reflects incident radiation of all wavelengths.

Explanation: An ideal black body is characterized by its ability to absorb all incident radiation, with an absorption power equal to one, and it is…

• A. Increasing the applied voltage.
• B. Decreasing the applied voltage.
• C. Increasing the amount of electric current.
• D. Decreasing the amount of electric current.

Explanation: In the Davison and Germer experiment, the velocity of electrons emitted from the electron gun is directly proportional to their kinetic…

• A. Length contraction.
• B. Space-time interval.
• C. Space-time geometry.
• D. Mass-energy relation.

Explanation: According to Einstein's general theory of relativity, gravity is not an ordinary force but a result of the curvature of space-time…

• A. Wave nature of light.
• B. Particle nature of light.
• C. Wave nature of electrons.
• D. Particle nature of electrons.

Explanation: The Davison-Germer experiment provided experimental evidence for the wave nature of electrons.

• A. String theory.
• B. Special theory of relativity.
• C. General theory of relativity.
• D. Galilean transformation theory.

Explanation: The correct answer is the Special theory of relativity. This theory specifically addresses non-accelerated, or inertial, frames of…

• A. Becomes zero.
• B. Remains the same.
• C. Shifts towards the longer wavelength.
• D. Shifts towards the shorter wavelength.

Explanation: The correct answer is Option D: shifts towards the shorter wavelength. This is explained by Wien's Displacement Law, which states that the…

• A. The more precisely the position is determined, the less precisely the momentum is known.
• B. The position and momentum of a particle can both be precisely determined simultaneously.
• C. The uncertainty in position and momentum are independent of each other.
• D. The uncertainty in position has no effect on the uncertainty in energy.

Explanation: The correct answer is that the more precisely the position of a particle is known, the less precisely its momentum can be known, and vice…

• A. Infinite
• B. Zero
• C. Negative
• D. Still not found

Explanation: The angular momentum of a photon is zero. A photon is a massless particle, and angular momentum is defined as the product of the moment of…

• A. Structure of metals only
• B. Nature of surface only
• C. Both metals and nature of surface
• D. Threshold frequency

Explanation: Work functions depend on the 'structure' and 'chemical composition of a surface'.

• A. 0, 0
• B. 1+, 0
• C. 1-, 0
• D. 1, 1

Explanation: A photon is massless, has no electric charge, and is a stable particle.

• A. 0.01eV sm-1
• B. 0.001eV s m-1
• C. 0.03eV s m-1
• D. 0.04eV s m-1

Explanation: Energy of photon, E=3MeV=3×10^6eVLinear momentum of the photon, p=E/cwhere c is the speed of light in vacuum p= 3×10^6 eV / 3×10^8…

• A. Momentum
• B. Frequency
• C. Mass
• D. All of these options are correct

Explanation: In quantum physics, wave-particle duality states that any particle or quantum phenomenon can be represented as either a particle or a…

• A. Remain constant
• B. Increase
• C. Decrease
• D. None of these

Explanation: The energy of photons is directly proportional to their frequency and inversely proportional to their wavelength, so lower-energy photons…

• A. Infinite rest mass
• B. Rest mass but no charge
• C. No rest mass & no charge
• D. A & C are correct

Explanation: A photon is simply a quantized particle of light and so has no rest mass nor charge.

• A. 5 x 10^14 Hz
• B. 6 x 10^14Hz
• C. 7 x 10(14) Hz
• D. 9 x 10(14) Hz

Explanation: v=f λf= v/λ = 3x10^8/500 x 10^-9 = 6x10^(14) Hz

• A. Emitted
• B. Absorbed
• C. Travelling
• D. All of these

Explanation: Since an X-ray photon has a large momentum (by the de Broglie relation), its uncertainty in momentum is low, but the uncertainty of…

• A. It varies directly with frequency.
• B. It is the same at all frequencies.
• C. It varies with frequency.
• D. None.

Explanation: Varies directly with frequency. We have a formula, E = hf where "h" is Planck's constant and "f" is the frequency, and "E" is the energy.