Name that wave behavior

Kerstin stands in the hallway outside an open gym door. She cannot see the band, but the music reaches her anyway, spreading around the doorway.

This topic and the one before it named four things a wave can do: reflection, refraction, diffraction, and interference. Real scenes rarely announce which one is happening. This lesson sorts scenes by what the wave actually did.

Each behavior has one telltale. The sort asks two questions: what did the wave meet, and what did it do there?

The music at the door met an opening and spread out beyond it. Spreading past a gap or an edge is diffraction's telltale.

The music spreads beyond the doorway. Spreading past a gap or an edge is diffraction's telltale.

A wave that meets a boundary it cannot pass and comes back has reflected. Coming back is reflection's telltale.

At a sea wall the ripples come back. Coming back is reflection's telltale.

A wave that crosses into a region where its speed changes, and changes direction there, has refracted. A new direction at the crossing is refraction's telltale.

Crossing onto the shallow steps, the fronts change direction. A new direction at a speed-change crossing is refraction's telltale.

Two overlapping sets of waves that produce a stable pattern of reinforced and canceled regions show interference. The stable pattern is its telltale.

Two steady sources make stable lanes. The stable pattern of reinforced and canceled regions is interference's telltale.

Every scene gives one telltale, and the telltale gives the name. Find what the wave met and what it did, and the name follows.

The summary, after the four drawn telltales: what the wave met, and what it did.

Ripples from a motorboat reach a sea wall and travel back out across the water. Which behavior is this?

The ripples met a boundary they could not pass, and they came back.

Reflection.

In a swimming pool, ripples cross from the deep end onto the shallow steps and change direction as they cross. Which behavior is this?

The ripples' speed changes where the water gets shallow, and their direction changes at the crossing.

Refraction.

Quick-fire drill

Lazlo shouts across a lake toward a rock cliff and hears his shout come back to him. Which behavior is this?

Music from a backyard party reaches Ilka through a narrow gap in a fence and spreads across the whole yard behind it. Which behavior is this?

Ocean ripples cross onto a shallow sandbar and change direction as they cross. Which behavior is this?

Two speakers on a stage play the same steady tone. Walking across the floor, Joby passes spots where the tone nearly disappears and spots where it comes through strongly, always at the same places. Which behavior is this?

A marching band turns onto the next street. From around the corner, with no straight path to the band, listeners still hear the music spread into their street. Which behavior is this?

A pulse sent along a rope reaches the post the rope is tied to and travels back along the rope. Which behavior is this?

Your turn

At a water park, two side-by-side jets drip steadily into a calm pool. Between them, lanes of big ripples alternate with lanes of nearly still water, holding their places. Which behavior is this?

Waves from a passing boat squeeze through the narrow entrance of a small cove and spread out to every corner of the cove. Which behavior is this?

Joby hears an announcement from around the corner of a school hallway, with no straight path to the speaker. Which telltale makes this diffraction rather than reflection?