Straight ripples cross slantwise onto a shallow shelf, where they slow down. Why does their travel direction change?
Nilo aims a beam of light at a glass block, slantwise. At the glass surface the beam kinks and carries on through the glass in a new direction.
OPT-024 named this behavior: refraction. This lesson explains why the direction changes.
Start with what changes at the boundary: the light's speed. Glass is optically denser than air, so the light slows as it enters the glass.
You have seen what a speed change does to a wave. For water waves crossing onto a shallow shelf, one end of each wavefront slowed before the other end, and the front swung around.
Light does exactly the same. The beam arrives slantwise, so one edge of each wavefront reaches the glass before the rest.
That edge slows first, while the rest of the front is still moving at full speed in the air.
The only new step since the waves topic is the name for light's speed change: optical density. Crossing into an optically denser medium is what slows the light.
A head-on arrival is the telling contrast. When the beam meets the boundary head-on, the whole wavefront reaches the glass at once. Every part slows together, nothing swings, and the direction holds.
So a slantwise arrival plus a speed change gives a bend. Take away either one, and the light goes straight.
A beam of light passes slantwise from air into still pond water. Explain why its direction changes at the surface.
Water is optically denser than air, so the light slows as it enters the water.
The beam arrives slantwise, so one edge of each wavefront enters the water first.
That edge slows first, while the rest of the front still moves at the air speed.
The speed difference across the front swings the front around.
The front swings toward a new direction, so the beam's path bends at the surface.
Maud aims the same beam straight down at the pond, head-on to the surface. The light still slows. Why does its direction NOT change?
Head-on, the whole wavefront reaches the surface at the same moment.
Every part of the front slows together.
No part gets ahead of any other, so nothing swings.
The front keeps its direction: the light slows but does not bend.
A beam of light passes slantwise from air into a glass block and bends. Why does the direction change?
Light crosses slantwise into an optically denser medium and bends. Which change in the light causes the bend?
Maud says: 'The bending happens only at the boundary. Once the whole wavefront is inside the glass, the light travels in a straight line again.' Is Maud correct?
Light slows as it crosses slantwise into a pool of water, and its path bends. Which statement explains the bend?
A laser beam travels through the middle of a large, uniform glass block, far from every surface. Why does its path stay straight there?
Which chain of causes puts the steps of refraction in the right order, for light entering glass slantwise?