Modern Physics: Relativity and Quantum Quiz

Grade 11 · Science · Quiz

Test your mastery of special relativity, the quantum nature of light and matter, and foundational modern physics concepts.

Questions

1. Which of the following is NOT a consequence of Einstein's special theory of relativity?

   1. Time dilation
   2. Length contraction
   3. Mass-energy equivalence
   4. Gravitational lensing of light
   Show answer

   Answer: Gravitational lensing of light

   Gravitational lensing is a consequence of General Relativity (which deals with gravity and curved spacetime), not Special Relativity. Special relativity covers time dilation, length contraction, and E = mc².

2. A photon has a frequency of 6×10¹⁴ Hz. What is its energy? (h = 6.626×10⁻³⁴ J·s)

   1. 3.98×10⁻¹⁹ J
   2. 6.63×10⁻³⁴ J
   3. 1.1×10⁻¹⁹ J
   4. 6×10¹⁴ J
   Show answer

   Answer: 3.98×10⁻¹⁹ J

   E = hf = (6.626×10⁻³⁴)(6×10¹⁴) = 3.98×10⁻¹⁹ J.

3. An electron has a momentum of 6.626×10⁻²⁴ kg·m/s. What is its de Broglie wavelength?

   1. 10⁻¹⁰ m
   2. 10⁻³⁴ m
   3. 6.626 m
   4. 10⁻⁷ m
   Show answer

   Answer: 10⁻¹⁰ m

   λ = h/p = (6.626×10⁻³⁴)/(6.626×10⁻²⁴) = 10⁻¹⁰ m = 1 Å, typical atomic scale.

4. In the photoelectric effect, what determines whether electrons are emitted at all?

   1. Intensity of the light
   2. Total power of the light beam
   3. Frequency of the light exceeding the threshold frequency
   4. Duration of light exposure
   Show answer

   Answer: Frequency of the light exceeding the threshold frequency

   The photoelectric effect has a threshold frequency f0 = φ/h. Below this frequency, no electrons are emitted regardless of intensity. The frequency must exceed this threshold.

5. What does Heisenberg's Uncertainty Principle fundamentally tell us?

   1. Measuring devices are always imperfect
   2. It is impossible in principle to simultaneously know both exact position and exact momentum
   3. Particles have no definite position
   4. Quantum particles are random and unpredictable
   Show answer

   Answer: It is impossible in principle to simultaneously know both exact position and exact momentum

   The Uncertainty Principle ΔxΔp ≥ ℏ/2 is a fundamental limit in nature, not just a measurement limitation. It reflects the wave-like nature of quantum particles.

6. At what speed would a spaceship need to travel for its Lorentz factor γ to equal 2?

   1. 0.5c
   2. 0.707c
   3. 0.866c
   4. 0.99c
   Show answer

   Answer: 0.866c

   γ = 2 means 1/√(1 - v²/c²) = 2, so 1 - v²/c² = 1/4, v²/c² = 3/4, v = (√3/2)c ≈ 0.866c.

7. Quantum mechanics predicts that an electron in an atom can have any arbitrary energy, not just specific discrete values.

   Show answer

   Answer: False

   Bohr's model (and quantum mechanics in general) shows electrons can only exist in quantized energy levels. They cannot have arbitrary energy values; only specific discrete energies are allowed.

8. The minimum energy required to eject an electron from a material's surface is called the work _____.

   Show answer

   Answer: function

   The work function φ (phi) is the minimum energy needed to liberate an electron from a material's surface. It is material-dependent and determines the threshold frequency for the photoelectric effect.

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