Light reflection simulator

What this simulator shows

Light travels in straight lines and bounces off shiny surfaces. In One mirror mode, drag the laser along the dotted arc or use the buttons. The beam hits a flat mirror, and the simulator draws the normal, a dashed line at right angles to the mirror, with the angle of incidence (the incoming beam) and the angle of reflection (the outgoing beam), both measured from the normal. In Periscope mode, you turn two mirrors inside a tube so that light from a bird travels over a brick wall, down the tube and out to an eye.

• The law of reflection: the angle of incidence equals the angle of reflection.
• Both angles are measured from the normal, not from the mirror's surface.
• The incoming beam, the reflected beam and the normal all lie in the same flat plane.
• A periscope uses two mirrors, each at 45°, to turn light through two right angles.

Why a simulator helps

With a real flashlight and mirror, the beam is hard to see and harder to measure. Here every ray and angle is drawn exactly, so children can test the rule many times in a minute. The target challenge turns the rule into a skill: once they trust it, they can aim the reflection where they want it.

Common misconceptions

Many students measure angles from the mirror's surface instead of from the normal. That still gives equal angles for a flat mirror, but it causes errors later with curved mirrors and with refraction, so it is worth getting right early. Younger children often think we see a mirror image because the mirror holds a picture, or that light only reflects from mirrors. Every object we see reflects some light into our eyes; mirrors are special because they reflect it neatly, all in the same direction. Another idea to check is that light "bends" off a mirror in a curve. It changes direction in one sharp turn at the surface.

A 10-minute reflection activity

• Set the laser to 30°. Ask the child to point to where the beam will go after the mirror.
• Check, then repeat at 60° and 10°. Ask them to state the rule in their own words.
• Hide the angles and press Challenge. Ask them to estimate the angle needed before moving the laser.
• Switch to Periscope. Ask why the light hits the tube wall, then let them fix the mirrors.
• Ask where periscopes are used: submarines, tanks, and crowds at parades.

Where this fits in school

• US, grade 4: NGSS 4-PS4-2 asks students to model how light reflecting from objects and entering the eye allows objects to be seen.
• US, middle school: NGSS MS-PS4-2 asks students to model how waves, including light, are reflected, absorbed or transmitted by materials.
• England, Year 3: pupils notice that light is reflected from surfaces. Year 6: pupils use the idea that light travels in straight lines to explain how we see things, and periscopes are a popular project.
• England, Key Stage 3: pupils use the ray model to explain reflection in mirrors.

Learning more

Light is part of Eurekami's science skill map. Lessons draw ray diagrams live, one line at a time, and daily practice brings back a few questions so ideas like the normal are remembered.