Estimated time: 45 minutes | Difficulty: Medium | Ref: KS2-LI-3
Learning objective: Investigate how mirrors reflect light; use ray diagrams
Use the pathway to build a clear mental model. Open each node and answer the check question.
Mirrors have a very smooth, shiny surface (usually glass coated with a thin layer of metal). When light hits this smooth surface, it bounces off in a very predictable way. This is called specular reflection. Unlike rough surfaces that scatter light, mirrors reflect light rays in an orderly pattern, which is why we see clear images.
Check: What makes a mirror's surface different from a rough surface like paper?
When light hits a mirror, it follows a simple rule: the angle of incidence equals the angle of reflection. This means light bounces off at the same angle it arrived at. If you shine a torch at a mirror at 45°, the light will bounce off at 45° on the other side. The "normal" is an imaginary line at right angles to the mirror surface that helps us measure these angles.
Check: If light hits a mirror at 30°, at what angle will it reflect?
When you look in a mirror, your reflection appears to be laterally inverted (reversed left to right). If you raise your right hand, your reflection appears to raise its left hand. The image also appears to be the same distance behind the mirror as you are in front of it. This is because the light rays create a virtual image that appears to come from behind the mirror.
Check: If you write the word "AMBULANCE" normally, how would it appear in a mirror?
Mirrors have many practical uses because we can predict how they reflect light. Periscopes use two mirrors to see around corners. Dentists use small mirrors to see inside mouths. Car wing mirrors help drivers see behind them. The Hubble Space Telescope uses mirrors to collect light from distant stars. Understanding reflection helps us design and use all these tools.
Check: Why might an ambulance have "AMBULANCE" written in mirror writing on its front?
A mirror is made of glass with a thin coating of shiny metal (usually aluminium or silver) on the back. The metal coating is what actually reflects the light - the glass just protects it and provides a smooth surface. The perfectly smooth surface means light reflects in a very predictable, regular way called specular reflection.
When light hits a mirror, it follows a precise rule called the law of reflection:
Angle of incidence = Angle of reflection
To understand this, we need to know about the normal - an imaginary line at right angles (90°) to the mirror surface:
If light hits a mirror at 40° to the normal, it will reflect at 40° to the normal on the other side. This predictable behaviour is what makes mirrors so useful!
When you look in a mirror, the image appears laterally inverted (reversed left to right). This is why:
The image also appears to be the same distance behind the mirror as the object is in front. This is called a virtual image because the light doesn't actually come from behind the mirror - it just appears to.
Scientists draw ray diagrams to show how light reflects from mirrors. A good ray diagram should include:
Understanding how mirrors work has countless applications: bathroom mirrors, car mirrors, telescopes, periscopes, laser equipment, dental tools, and much more. The law of reflection allows engineers to design precise optical equipment and helps us understand how we see the world around us.
Have you noticed that ambulances in the UK have "AMBULANCE" written in reverse (mirror writing) on the front? This is a clever use of the law of reflection! When a driver looks in their rear-view mirror, they see the word the correct way around: "AMBULANCE". The mirror reverses the already-reversed text, making it readable. This helps drivers quickly identify approaching emergency vehicles and move out of the way. The word appears laterally inverted in the mirror, so writing it backwards in the first place cancels out the effect!
Periscopes use two mirrors positioned at 45° angles to allow people to see over obstacles or around corners. British submarines have used periscopes since the early 1900s. Light from above the water surface hits the first mirror at 45°, reflects at 45° (following the law of reflection) down to the second mirror, which reflects it into the observer's eyes. The Royal Navy's submarines at HMNB Clyde in Scotland use modern periscopes that work on exactly the same principle. You can make a simple periscope with two small mirrors and a cardboard tube!
Edinburgh's Camera Obscura and World of Illusions, located on the Royal Mile near Edinburgh Castle, is one of Scotland's oldest tourist attractions (opened in 1853). While it uses lenses rather than mirrors, the attraction includes many mirror-based optical illusions that demonstrate reflection principles. The hall of mirrors creates infinite reflections by placing mirrors opposite each other - each reflection creates another reflection, seemingly going on forever. The angled mirrors create distorted images that make you look tall, short, wide, or thin, all by reflecting light at different angles.
The Isaac Newton Telescope (INT) on La Palma in the Canary Islands is operated by the UK's Isaac Newton Group of Telescopes. Named after the British scientist who studied light extensively, this telescope uses large mirrors to collect and focus light from distant stars and galaxies. Instead of a lens, it uses a 2.54-metre diameter mirror! The mirror's precise curved shape focuses light following reflection principles. Newton himself built the first practical reflecting telescope in 1668, using his understanding of the law of reflection. Today's astronomers use this same principle with much larger mirrors.
Answer all questions, then check your answers. Your quiz result is saved on this device.
Wrong: "The angle of incidence is 60° because that's the angle between the ray and the mirror."
Right: Angles of incidence and reflection are ALWAYS measured from the normal (the line at 90° to the mirror), not from the mirror surface. If a ray appears to hit the mirror at 60° from the surface, the angle of incidence is actually 30° (since 90° - 60° = 30°). Always draw and measure from the normal!
Wrong: "The mirror creates light that allows me to see my reflection."
Right: Mirrors don't produce or create light - they only reflect it! Without a light source illuminating you, a mirror would show nothing. The mirror simply bounces light rays back in a predictable pattern. Put a mirror in complete darkness and it's useless - there's no light to reflect.
Wrong: Drawing rays as simple lines without arrows.
Right: Ray diagrams MUST include arrows to show the direction light is travelling. The incident ray arrow should point TOWARDS the mirror, and the reflected ray arrow should point AWAY from the mirror. Without arrows, your diagram doesn't show which way the light is moving, which defeats the purpose of the diagram.
Wrong: "When I look in a mirror, there's actually another version of me behind the glass."
Right: The image you see is a virtual image - it appears to be behind the mirror, but there's nothing actually there! The light rays reflect off the mirror and enter your eyes. Your brain interprets these rays as if they came from behind the mirror, creating the illusion of depth. If you look behind a mirror, you won't find your reflection there!