Light: Reflection, Refraction, and Straight Lines — Year 6 Lesson Plan
National Curriculum: Science KS2 (Y6) — Light: recognise that light appears to travel in straight lines; use the idea that light travels in straight lines to explain that objects are seen because they give out or reflect light into the eye; explain why shadows have the same shape as the objects that cast them and to predict the size of shadows when the light source or object is moved.
Overview
This lesson extends pupils' Year 3 understanding that light travels in straight lines and that shadows form when light is blocked by opaque objects. Year 6 pupils now explore with greater precision and explanation how light is seen, how it reflects from surfaces following the law of reflection, and how it changes direction when it passes from one medium to another (refraction). Pupils carry out quantitative investigations and use their results to draw and test generalisations, working at the upper end of the KS2 science enquiry expectations.
Learning Objectives
- Explain that light travels in straight lines from a source to the eye or from a source to a surface and then to the eye.
- Use the idea of straight-line travel to explain why shadows have the same shape as the objects that cast them.
- Investigate and explain the law of reflection: the angle of incidence equals the angle of reflection.
- Describe and explain refraction as the bending of light when it passes from one medium to another.
Key Vocabulary
Suggested Lesson Structure
Pose the mystery question: if light travels in straight lines, how does a periscope make it possible to see around corners? Show a diagram of a periscope with the mirrors hidden. Ask pairs to discuss how they think it works. Take ideas without confirming. Then show a simple torch-and-mirror demonstration: shine a torch at a mirror on the wall and ask pupils to trace the path of light from torch to mirror to wall. Establish that the light has changed direction at the mirror — it has been reflected. Link to the Year 3 work on shadows as confirmation that light travels in straight lines.
Teach the law of reflection using a ray-diagram approach. Draw a mirror on the board, a perpendicular normal line, and an incoming ray. Measure and label the angle of incidence (i) and the angle of reflection (r). State the law clearly: angle i always equals angle r. Model drawing two examples with different angles. Then introduce refraction: show the classic demonstration of a pencil appearing bent in a glass of water. Explain that light slows down when it passes from air into water, and this slowing causes the change in direction. Draw a refraction diagram showing the ray bending toward the normal as it enters the denser medium.
Investigation 1 (reflection): Pupils use a mirror, a ray box or torch with a slit, and a protractor to measure the angle of incidence and angle of reflection for five different incident ray angles. They record results in a table. The teacher circulates and asks: what pattern do you notice? Investigation 2 (whole class): Pupils observe a straw in a beaker of water from different angles and draw what they see. Discuss: why does the straw appear to bend? Why does it appear to jump when you look straight down? What happens when you add more water?
Pupils complete a graph plotting angle of incidence (x-axis) against angle of reflection (y-axis) for their reflection data, draw a line of best fit, and write a conclusion: My investigation shows that... This tells me that... I am confident/not confident in my results because... A challenge question is available for pupils who finish early: draw a ray diagram showing how a periscope uses two mirrors to allow someone to see over a wall, labelling the angles of incidence and reflection.
Return to the opening question: how does a periscope work? Ask a pupil to explain it using the correct vocabulary. Then pose a new question to stimulate thinking: why do diamonds sparkle? (Total internal reflection at the correct angle — teachers can give a brief, age-appropriate explanation.) Close by asking pupils to write one sentence summarising what they now know about how light behaves that they did not know at the start of the lesson.
Common Misconceptions
- Pupils often believe they see objects because light travels from their eyes to the object. In fact, light travels from a source to the object and is reflected into the eye. This is a deeply rooted misconception — the eye is a receiver, not a projector.
- When studying refraction, pupils often describe the light as bending randomly. They need to understand that the direction of bending is predictable: light bends toward the normal when entering a denser medium (e.g. air to water) and away from the normal when entering a less dense medium (e.g. water to air).
Prior Knowledge
Pupils should already be able to:
- Understanding from Year 3 that light travels in straight lines, that dark is the absence of light, and that shadows are formed when opaque objects block light.
- Ability to measure angles using a protractor and to plot results on a graph.
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