In a ripple tank, straight ripples cross slantwise from deep water onto a shallow shelf. At the depth line their path kinks: beyond it, the ripples head in a new direction.
No barrier, no bounce. The wave crossed into a medium where its speed is different, and its travel direction bent. Why?
Two facts are already in hand: the medium sets the wave's speed, and ripples travel more slowly in shallow water.
Now watch one wavefront arrive slantwise at the depth line. One end of the front reaches the shallow water first.
That end slows down at once. The other end is still in deep water, still moving fast.
For a moment, one end of the front crawls while the other races, the way a row of walkers swings around when the walkers at one end slow down.
By the time the whole front is in the shallow water, it faces a new direction. The travel direction bends because the part of the wavefront that enters the new medium first changes speed first, swinging the whole wavefront toward a new direction.
Refraction needs two things: a speed change, and a slantwise arrival. A front that crosses head-on changes speed and wavelength, but every part of it changes together, so nothing swings and the direction holds.
Straight ripples cross slantwise from deep water into shallow water, where they travel more slowly. What happens to their travel direction, and why?
The end of each wavefront that enters the shallow water first slows down first.
The rest of the front, still in deep water, keeps its speed for a moment longer, so the front swings around the slowed end.
The travel direction bends at the line: the wave refracts, because one end of each front changes speed before the other.
Straight ripples cross slantwise from a shallow shelf into deep water, where they travel faster. Does the direction still change?
The end of each front that enters the deep water first speeds up first.
That end races ahead while the rest of the front still crawls, so the front swings again, this time around the slow end still on the shelf.
Yes. The direction changes at the line whenever the speed changes and the arrival is slantwise.
Straight ripples cross slantwise into water where their speed is different. What happens to their travel direction?
Straight ripples cross slantwise onto a shallow shelf, where they slow down. Why does their travel direction change?
Fenna says: 'A wavefront that crosses a boundary head-on changes speed but keeps its direction.' Is Fenna correct?
Which situation shows refraction?
Straight ripples cross a depth line head-on: each wavefront is parallel to the line. The ripples slow beyond it. What happens to their travel direction?
Straight ripples cross slantwise into water where they travel faster. Which statement explains what happens at the boundary?