Quenby shines a laser pointer through a narrow slit cut in a piece of cardboard. The spot on the far wall is not a thin stripe: the light has spread out.
This lesson collects the evidence about what light is. You already know how waves behave from the waves topic. The question is whether light behaves that way too.
In the waves topic, water waves showed four behaviors: they reflect, they refract, they diffract, and they interfere.
Spreading out after a narrow gap is diffraction, and diffraction is a wave behavior.
Quenby's light spread out after the slit, exactly as water ripples spread out beyond a harbor opening.
Light does exactly what the water waves did.
Light reflects off surfaces, as a ripple reflects off a pool wall.
Light refracts where it enters a new material, as ripples refract crossing into shallow water.
Light from two nearby openings even builds the reinforced-and-canceled pattern of interference.
A flashlight beam bounces off a bathroom mirror. A rope pulse bounces back from a wall. Name the wave behavior both show.
The beam meets a surface it cannot pass through, and it bounces back.
The rope pulse does the same at the wall.
Bouncing back at a boundary is reflection.
Both show reflection, and light shows it just as the mechanical wave does.
A beam of light bends as it enters a glass block. Ripples change direction as they cross into shallow water. Name the wave behavior both show.
In each case the wave crosses into a region where it travels at a different speed.
In each case the travel direction bends at the crossing.
Bending at a speed change is refraction.
Both show refraction, and light shows it just as the water wave does.
Light from a streetlight passes through a narrow gap between two fence boards and spreads out beyond them. Which wave behavior is this?
A laser beam bounces off a polished steel door. Water ripples bounce off a pool's side wall. Which wave behavior do both show?
Selby says: 'Light spreading out after passing through a narrow slit is the same wave behavior as water ripples spreading out beyond a harbor opening.' Is Selby correct?
Which observation is evidence that light travels as a wave?
A beam of light changes direction as it passes from air into water. Ripples change direction as they cross from deep water into shallow water. Which wave behavior do both show?
Sound bends around an open door into a hallway. Which observation of light shows the same wave behavior?