Fourth Grade · Science · week 13

Light reflection paths

Describe light as traveling in straight lines and reflecting off surfaces along a predictable path, using a mirror investigation.

Light travels outward from its source in straight lines called light rays, and it keeps going straight until it hits something. When light hits a smooth, shiny surface like a mirror, it bounces off in a new straight-line direction instead of stopping. That bounce is called reflection, and it follows a predictable path.

You can trace a light path with a flashlight and a mirror. Shine a beam at a mirror from one angle, and the reflected beam bounces off at a matching angle on the other side, almost like a ball bouncing off a wall. Once you know that pattern, you can predict where a reflected beam will go before you even test it.

📋 For the teacher
Teach it (10–15 min):
  • In a slightly dim room, shine a flashlight at a small hand mirror and trace the path of the reflected beam onto a wall or piece of paper.
  • Change the angle of the flashlight and ask your child to predict which way the reflected beam will move before you try it.
  • Use two mirrors if you have them to bounce a beam around a corner, showing that reflection can redirect light more than once.
  • Connect this back to real life: rearview mirrors, periscopes, and even how you see your own reflection all rely on this same predictable bounce.
Talk about it:
  • What did you notice about the angle the light arrived at compared to the angle it left at?
  • Could you predict where the reflected beam would go before testing it? How?
  • Where do you use mirrors or reflection in everyday life?

Mastery looks like: They can predict the general path of a reflected light beam off a mirror and explain that reflection follows a matching-angle pattern.

Common stumbles: Thinking reflected light bounces off in a random direction; forgetting that light travels in a straight line both before and after it reflects.

Homework for this lessonType it, write it with a stylus, or print it for pencil & paper.open →
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