Waves · Chapter 4: Reflection and echoes

Year 11 Science · About 16 minutes with activities · Turn your sound on

Chapter 4 · Reflection and echoes

Hunting in the darkthe bat can’t see the moth

Squeak out

Echo back

Shorter echo time= the moth is closer

Straightwavefronts, e.g. ocean swell

Ray ⟂ wavefronts

Circularwavefronts from a point source

Almost flatrays almost parallel

Mirrorone ray

Specularsmooth surface

Diffuserough surface

Incident ray

Normalat 90° to the mirror

Reflected ray

i = r

Satellite

Ground station

Destination

Ship with sonar

Ping down

Echo up

Seabed

Chapter 4 recap

Wavefronts join matching points (e.g. crests), one wavelength apart. Rays show the direction of travel, perpendicular to the wavefronts.
Specular reflection: smooth surface. Diffuse: rough surface. Law of reflection: angle of incidence = angle of reflection, both measured from the normal.
Satellites reflect radio waves to their destination (36 000 km up: 0.24 s up and back). Echoes: d = v × t ÷ 2, because t is there and back.
Next: Chapter 5 · Refraction and total internal reflection

How does a bat find a moth in the dark?

Chapter 4 · About 16 minutes · sound on

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