Reflection & Refraction of Light

Reflection is light bouncing off a mirror. By the law of reflection the angles of incidence and reflection are equal, measured from the normal. Refraction is the bend when light enters another medium; from air into water it bends toward the normal so the refracted angle is smaller. Turn the incidence-angle slider to watch reflection and refraction change.

Light on a Mirror — Reflection

Incidence angle40°

💡 Law of Reflection

①Angle of incidence = angle of reflection (always)

②Angles measured from the normal

③Why we see ourselves in a mirror

④Light reflects regularly off smooth surfaces (specular reflection)

Why Light Bends in Water — Refraction

🔍 What is Refraction?

①Light bends when crossing into a different medium

②Air → water: bends toward the normal (refraction < incidence)

③Water → air: bends away from the normal (refraction > incidence)

④Pool bottoms appear shallower because of refraction!

Laws of Reflection and Refraction

Law of Reflection

Angle of incidence = angle of reflection

Reflection angles are always equal at a mirror

Refraction Rule

Light: faster medium → slower medium → bends toward normal

Air → water/glass: refraction angle < incidence angle

🌈 Refraction in Daily Life

①Straws appear bent in water

②Rainbows: refraction + dispersion in raindrops

③Mirages: air-temperature differences refract light

④Glasses lenses use refraction to focus

Exam Key Points

Core Summary

Reflection: i = r | Refraction: bends when medium changes

Law of reflection always holds; refraction depends on the medium

🎯 Exam Key Points

①Law of reflection: i = r

②Specular vs diffuse: smooth vs rough surface

③Air→water: refraction < incidence

④Water→air: refraction > incidence

⑤Total internal reflection: incidence > critical → fully reflected

Examples and Unit Test

Example 1

Light hits a mirror at an angle of incidence of 40°. What is the angle of reflection?

By the law of reflection, the angle of incidence and the angle of reflection are always equal (measured from the normal).

Since the angle of incidence is 40°, the angle of reflection is also 40°.

▸ 40°

By the law of reflection, the angle of incidence equals the angle of reflection (from the normal).

Example 2

When light passes at an angle from air into water, is the angle of refraction larger or smaller than the angle of incidence, and why?

When light goes from a faster medium (air) into a slower medium (water), it bends toward the normal.

Because it bends toward the normal, the angle of refraction is smaller than the angle of incidence.

▸ The angle of refraction is smaller than the angle of incidence (it bends toward the normal)

From air to water the angle of refraction is smaller than incidence (toward the normal); from water to air it is the opposite.

Unit-test style

Which statement about reflection and refraction of light is correct?

①When light reflects, the angle of incidence is always larger than the angle of reflection

②In reflection, the angle of incidence and the angle of reflection are always equal

③When light goes from air into water, the angle of refraction is larger than the angle of incidence

④Angles are measured from the surface of the mirror

⑤Light does not bend even when it enters a different material

▸ ② In reflection, the angle of incidence and the angle of reflection are always equal

By the law of reflection, the angle of incidence and reflection are always equal, so ② is correct.

In reflection incidence equals reflection (①), from air to water the angle of refraction is smaller than incidence (③), angles are measured from the normal (④), and light refracts when the medium changes (⑤).

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