Lesson · P.4.2

Light, reflection and refraction

Light as an electromagnetic wave that needs no medium, and the two rules the HESI physics subtest expects at every boundary: reflection at a matching angle, and refraction whenever light's speed changes between media.

ObjectiveP.4.2Read4 minExam weightWaves, Sound and Light ≈ 20% of Physics

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What you will be able to do

You can explain why light needs no medium to travel, unlike sound and other mechanical waves.
You can apply the law of reflection to find an unknown angle at a reflecting surface.
You can predict which way a light ray bends when it crosses into a medium where it slows down or speeds up.

What the lesson concludes

Light is an electromagnetic wave that travels through a vacuum at 3.0 × 10⁸ m/s and needs no medium to travel through, unlike sound.
The law of reflection states that the angle of incidence equals the angle of reflection, both measured from the normal, not the surface.
Refraction is the bending of light caused by a change in its speed when it crosses from one medium into another.
Light bends toward the normal when it slows down entering a denser medium, and away from the normal when it speeds up leaving one.
A ray that meets a boundary straight along the normal changes speed but does not change direction.