Interference patterns are important for showing how light behaves like a wave. When two or more light waves overlap, they can mix together in different ways. This mixing creates patterns that we can see.

Constructive Interference

• This happens when the waves align perfectly.
• The height of the combined wave gets bigger.
• For example, if you have two waves that are both 2 units tall, when they come together, the new wave can be 4 units tall.

This creates bright spots on a screen where the light is strongest.

Destructive Interference

• This occurs when the waves do not align properly.
• The height of the combined wave gets smaller and might even cancel each other out completely.
• For example, if one wave is 2 units tall and the other wave is -2 units tall, they can cancel each other, leading to a height of 0 units.

This results in dark spots on the pattern.

Evidence from Experiments

• One famous experiment that shows this is the double-slit experiment by Thomas Young. In this test, light goes through two narrow openings that are close together.

This creates a series of bright and dark stripes on a screen.

• The spacing of these stripes depends on the wavelength (the distance between the peaks of the wave) of the light and how far apart the slits are.

The formula for figuring out how far apart the stripes are looks like this: $\Delta y = \frac{\lambda L}{d}$

Here, $L$ is the distance from the slits to the screen.

These patterns show that light behaves like a wave, which is different from how particles act. They help us understand how waves mix together.