Wavelets that explain mirrors and bending light

Science · Waves, Light & Sound · ages 18-19

Name ______________________ Date ____________

State the law of reflection.
- Angles are measured from the surface instead
- Angles match, measured from the normal
- Incident light never leaves
What does Huygens principle claim?
- Each front point emits wavelets shaping the next front
- Light travels only in straight rays
- Wavefronts never move
Crossing into glass changes the light frequency.
Circle one: True False
With c at 300 million metres per second and glass at n of 1.5, what is v in the glass in the same units?
Answer: ______________
What is n of a material?
- v over c
- c times wavelength
- c over v
Why does wavelength shrink while frequency holds?
- Slower speed packs the fixed rate of crests tighter
- Glass eats some crests
- Sources speed up inside
A student measures both angles from the surface. What is the error?
- Surface readings are the standard
- Glass has no normal line
- Angles belong to the normal, so every reading is off
How does Huygens reasoning produce Snell law?
- Assuming light speeds up inside glass
- Matching arrival times along the boundary forces the sine rule
- Measuring brightness alone

Answer key

For grown-ups. Fold this page away before handing over the rest.

Angles match, measured from the normal · Incoming and outgoing angles mirror across the normal.
Each front point emits wavelets shaping the next front · New fronts grow as tangent surfaces to many small wavelets.
False · The source launch rate is untouched by the crossing.
200 · Divide c by n: 300 divided by 1.5 is 200.
c over v · The index compares vacuum speed to material speed.
Slower speed packs the fixed rate of crests tighter · Equal launch rate at lower speed means tighter spacing.
Angles belong to the normal, so every reading is off · Both laws quote angles against the normal, not the surface.
Matching arrival times along the boundary forces the sine rule · Wavelets on both sides must stay in step along the edge.