X-Ray Diffraction and the Bragg Condition · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Reading atomic spacing from X-ray spots

Science · Waves, Light & Sound · ages 20-22
Name ______________________   Date ____________

  1. Why use X-rays instead of visible light on crystals?

    • X-rays are brighter to the eye
    • Crystals absorb visible light fully
    • Atomic planes are far smaller than visible wavelengths

  2. What is the Bragg condition?

    • Spacing equals wavelength times angle
    • Whole wavelengths equal twice spacing times sine of angle
    • Angle equals twice spacing over order

  3. In the Bragg law the angle is measured from the surface normal.

    Circle one:   True   False

  4. Wider plane spacings move the spots which way?

    • Toward smaller angles
    • Toward larger angles
    • They stay exactly fixed

  5. Planes 0.252 nm apart give a second-order spot at 30 degrees from the surface. Type the wavelength in nm.

    Answer: ______________

  6. What do spot positions and spot brightness each tell you?

    • Both give only the temperature
    • Positions give spacing and geometry, brightness gives what sits at lattice points
    • Positions give color, brightness gives size

  7. Why do only a few diffraction orders ever appear?

    • Sine caps at one, so higher orders run out of angles
    • Crystals melt before higher orders form
    • Higher orders overlap into invisibility

  8. A student expects a smooth glow from a crystal. What is wrong?

    • Crystals block all X-rays
    • Detectors cannot see smooth glows
    • Only special angles satisfy Bragg, so spots appear
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Answer key

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

Reading atomic spacing from X-ray spots W1-mt_qEDplGeIkB-s1

  1. Atomic planes are far smaller than visible wavelengths · Only a probe near 0.1 nm notices atomic-scale structure.
  2. Whole wavelengths equal twice spacing times sine of angle · Crest meets crest exactly when the extra path is a whole number of wavelengths.
  3. False · The Bragg angle is measured from the surface itself, unlike the optics habit.
  4. Toward smaller angles · A bigger spacing needs a smaller sine to hold the same wavelength match.
  5. 0.126 · Twice 0.252 times sine of 30 degrees, divided by order 2, gives 0.126 nm.
  6. Positions give spacing and geometry, brightness gives what sits at lattice points · Geometry sets where spots land, while contents set how bright each shines.
  7. Sine caps at one, so higher orders run out of angles · Each higher order needs a larger sine, and sine cannot pass one.
  8. Only special angles satisfy Bragg, so spots appear · Constructive matches happen only at select angles, giving sharp spots.
Worksheet · LightMySky