اردو

Home / Practice / Class 12 / Physics / Dawn of modern physics

Dawn of modern physics

Written by Dr. Hamza Farooq (Physics)

8 Class 12 Physics questions with answers and explanations.

Printable worksheet with answer key

All questions with answers
  1. In the photoelectric effect, the maximum kinetic energy of emitted electrons depends on the:

    • 1 Frequency of light
    • 2 Area of metal
    • 3 Time of exposure
    • 4 Intensity of light
    Show answer

    Correct answer: Frequency of light

    KE max = h f - work function.

    Report a mistake

  2. The energy of a photon is given by:

    • 1 h f
    • 2 h f²
    • 3 h / f
    • 4 f / h
    Show answer

    Correct answer: h f

    E = h f.

    Report a mistake

  3. de Broglie wavelength is:

    • 1 p / h
    • 2 h / p
    • 3 h / E
    • 4 h p
    Show answer

    Correct answer: h / p

    wavelength = h / momentum.

    Report a mistake

  4. Compton scattering shows that light behaves as:

    • 1 Particles
    • 2 Only waves
    • 3 Neutral rays
    • 4 Sound
    Show answer

    Correct answer: Particles

    It treats a photon as a particle with momentum.

    Report a mistake

  5. Einstein's famous mass energy relation is:

    • 1 E = m c
    • 2 E = m c²
    • 3 E = m² c
    • 4 E = c / m
    Show answer

    Correct answer: E = m c²

    E = m c².

    Report a mistake

  6. The minimum frequency of light needed to emit photoelectrons is the:

    • 1 Beat frequency
    • 2 Threshold frequency
    • 3 Resonant frequency
    • 4 Critical frequency
    Show answer

    Correct answer: Threshold frequency

    Below it no emission occurs.

    Report a mistake

  7. Heisenberg's uncertainty principle says we cannot know exactly both the position and the:

    • 1 Charge
    • 2 Momentum
    • 3 Colour
    • 4 Mass
    Show answer

    Correct answer: Momentum

    The product of the uncertainties has a minimum.

    Report a mistake

  8. Pair production needs a photon of energy at least:

    • 1 13.6 eV
    • 2 1.02 MeV
    • 3 931 MeV
    • 4 0.51 MeV
    Show answer

    Correct answer: 1.02 MeV

    It must supply the rest mass of an electron and a positron.

    Report a mistake

More Physics topics