Mon Prof Augmenté
Two slits make light bands
Age 18 · Physics
Green laser light passes through two narrow slits and lands on a screen as alternating bright and dark vertical bands. The bright bands appear where waves from the slits arrive together, and dark bands where they arrive out of step.
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In the picture
- Laser source: sends a narrow green beam toward the slits.
- Barrier with two thin slits: lets the beam become two overlapping sets of waves.
- Central bright band: waves from both slits arrive in step.
- Dark band: waves from the two slits arrive half a wavelength out of step.
- Crossing arcs: two wavefronts meet; their step relation changes from one place to the next.
Examples
- Colourful reflections on a soap bubble.
- The shimmering colours on a CD or DVD surface.
Key takeaways
- Bright bands occur when the path difference is a whole number of wavelengths.
- Dark bands occur when the path difference is half a wavelength.
Quiz: Two slits make light bands (Age 18)
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In a double-slit pattern, what path difference makes a bright band?
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In a double-slit pattern, what path difference makes a dark band?
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Why are there alternating bright and dark bands on the screen?
The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.
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