de Broglie Waves and Electron Diffraction · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

When particles behave like waves

Science · Waves, Light & Sound · ages 17-18
Name ______________________   Date ____________

  1. An electron's momentum doubles while h stays fixed. What happens to its wavelength?

    • It doubles
    • It halves
    • It stays the same

  2. Which observation proves that electrons behave as waves?

    • Light casting sharp shadows
    • Rings from electrons through graphite
    • Echoes bouncing off a wall

  3. A flying cricket ball has a wavelength far too tiny to ever show diffraction.

    Circle one:   True   False

  4. A flying cricket ball has a wavelength far too tiny to ever show diffraction. True or false?

    Circle one:   True   False

  5. The accelerating voltage is quadrupled. What happens to the electron's de Broglie wavelength?

    • Halved
    • Doubled
    • Quartered
    • Unchanged

  6. An electron has momentum 6.63e-24 kg m/s. Use h = 6.63e-34 J s with lambda = h / p. What is its de Broglie wavelength in metres?

    Answer: ______________

  7. Electrons diffract through graphite into rings. The voltage is raised. What happens to the rings?

    • They grow wider
    • They vanish at once
    • They shrink inward

  8. Electrons diffract through graphite into rings. The voltage is raised. What happens to the rings?

    • They shrink
    • They grow
    • They vanish
    • They stay the same

  9. Ben expects electron diffraction at a wide open doorway. Why will he see nothing?

    • The gaps must be near atomic size
    • Electrons move too slowly to diffract
    • Crystals absorb every electron

  10. The accelerating voltage drops to one quarter of its value. What happens to the wavelength?

    • It doubles
    • It halves
    • It stays the same
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Answer key

For grown-ups. Fold this page away before handing over the rest.

When particles behave like waves W1-mt_Y8NthsmPcv-s1

  1. It halves · Wavelength is h over momentum, so twice the bottom means half the wavelength.
  2. Rings from electrons through graphite · Diffraction rings need interfering waves, and the electrons draw them.
  3. True · Its huge momentum makes its wavelength absurdly smaller than any object it meets.
  4. True · Its huge mass makes its wavelength absurdly smaller than any object it meets.
  5. Halved · Momentum grows as the square root of voltage, so four times the voltage halves the wavelength.
  6. 1e-10 · Divide h by p: 6.63e-34 / 6.63e-24 = 1.0e-10 m.
  7. They shrink inward · Higher voltage shortens the wavelength, and shorter waves bend through smaller angles.
  8. They shrink · Higher voltage shortens the wavelength, and shorter waves diffract through smaller angles.
  9. The gaps must be near atomic size · Electron wavelengths sit near 1e-10 m, so only atomic-scale gaps can reveal them.
  10. It doubles · Momentum follows the square root of voltage, so quarter voltage halves momentum and doubles wavelength.
Worksheet · LightMySky