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Universe in the Classroom

The Welsh Government funding for Universe in the Classroom ended in June 2018. We have left this site available as an archive of the project.

How Light Travels

Light is our window, not only to the distant Universe, but to the entire world around us. How Light Travels is an enquiry-based activity in which students explore how light behaves, using common items such as torches, mirrors and a mixture of opaque, translucent and transparent objects. Specifically the class will learn that light moves in straight lines and can be reflected, and that effect of transparent and opaque objects on light.

How Light Travels Teacher Guide

How Light Travels Student Worksheet

Full Instructions

Learning Objectives
  • Understand that light travels in straight lines
  • Understand the term reflection and demonstrate the phenomenon
  • Understand how a reflector telescope works
  • Understand that light can travel through transparent objects and cannot travel through opaque objects.

Per group:

  • Bright torch
  • x2 hand-held mirrors
  • Piece of card (or other opaque object)
  • Cling Film (or other transparent object)

Per student:

  • Ruler
  • Pencil
  • Diagram of a 0.4-metre telescope (Appendix 1)
Background Information

Light travels in straight lines. When light hits an object, it is reflected and enters our eyes, this is how we see the object.

When you think of reflection, it is likely that you think about mirrors. Mirrors reflect all of the light that hits them. That is the reason you can see yourself so clearly in a mirror.

All objects we see either emit or reflect light, this is how we see them. For example, the ocean reflects light, although not as much of it as a mirror. If look down into the ocean, you will not see a clear reflection of yourself, but you will see a reflection of the sky. When light bounces off an object, the angle of reflection is equal to the angle of incidence.

Transparent objects allow you to see clearly through them; some examples are windows and glasses. Translucent objects only let some light through them so you cannot see clearly through a translucent object; some examples are plastic bottles and moving water. Opaque objects do not let any light through them s you cannot see through them; some examples of opaque objects are walls and tables.

  1. Split the class into groups of three or four.

  2. Ask the students how light travels. Write the following questions on the board: a. How does light travel? b. Can light travel through objects? c. Can light change direction?

  3. Tell the students they will use the materials provided to answer these questions. Give each group a bright torch, two mirrors, some cling film and a piece of card.

Note: If you do not have enough materials to provide for several groups, or you are working with younger, less independent students, simply skip to Step 5.

  1. Give the students 10-minutes to experiment with their materials and try to answer the questions on the board.
    • Can they direct their light to a target on the wall? What happens if they involve the mirrors and other props?
    • How is the light affected by different materials?
    • How many of their props can they use at the same time and still get their light to reach target on the wall?

Volunteers demonstrate how light can be directed using reflective material such as mirrors.

  1. Next, ask the students to sit down and dim the lights.

  2. Ask for a volunteer. Turn on your bright torch and ask the volunteer to point the torch beam at a target on a wall. Ask the children whether they think the light is travelling in a straight line or wiggly line.

Note: If the beam of the torch is not visible, put your hand between the torch and target at various points to demonstrate the path of the light.

  1. Ask a second volunteer to hold a piece of card between the torch and target. Make sure the class can see the target — is the light still reaching the target? Why not?

  2. Swap the card for a piece of cling film. Ask the volunteer to stretch the cling film tightly and hold it between the torch and target. Is the light reaching the target now? What is different?

  3. Explain that objects that allow light to travel through them are called ‘transparent’ and objects that do not allow light to pass through them are called ‘opaque’. Write these two terms on the board.

  4. Now ask for another volunteer to join you. Give the volunteer a mirror and point the beam of your torch away from the target. Ask the volunteer if they can catch the beam and bounce it off the mirror so it hits the target.

  5. Once they have successfully aimed the beam at the target, ask for another volunteer and hand them a second mirror. Ask them to work together to try to direct the beam to the target using both mirrors.

Volunteers demonstrate Step 11 of the **How Light Travels** activity.

  1. Explain that when light bounces off a surface it is called reflection. Write this word on the board.

  2. Explain that some telescopes use mirrors to collect light from stars and other objects in the Universe.

  3. Now hand each student a Reflecting Telescope worksheet (Appendix 1). Ask them to draw the path light takes from the stars to the eye, through the telescope, on their Diagram of a 1-metre Telescope (the result should look similar to the image below), and to fill in the gaps for Question 2.

Diagram showing the path cosmic light takes through a reflector telescope to the eyepiece.


Now that your students understand how a telescope works, invite them to use a powerful reflector telescope to take pictures of some of the wonders of the cosmos — the LCOGT robotic telescopes. The light from these objects has travelled many years before being captured by our telescopes, just for your pleasure!

If you don’t have access to the robotic telescopes, explore the LCOGT Archive to see all the images collected by LCOGT telescopes, or the Image Gallery for a selection of the most impressive.

KS2 Science in the Welsh National Curriculum “How things work: how light travels and how this can be used.”