3.2 Reflection
Summary: In everyday life, many objects create reflections, like in Figure 1. Shop windows, pans, car doors … but why do some surfaces create reflections and not others? Tags: science oxford-science student-book-7 physics Created: 2026-05-19 Last Updated: 2026-05-19
After this topic, you will be able to:
- describe what happens when Light is reflected
- use the law of reflection to explain how images are formed in a plane mirror
- describe the difference between specular reflection and diffuse reflection.
Think back
- Where do you see your reflection?
- Complete the sentence: ‘Light travels in blank lines.’
- What do you call a reflection of Sound?
Key idea Light reflects off surfaces. Ray diagrams show how this happens. You can only see your image in surfaces (e.g. a mirror) that reflect light in a regular way.
Key words image, virtual, plane, normal, angle of incidence, angle of reflection, incident ray, reflected ray, law of reflection, specular reflection, diffuse reflection
In everyday life, many objects create reflections, like in Figure 1**. Shop windows, pans, car doors … but why do some surfaces create reflections and not others?**
Figure 1You might be able to see your reflection in a window.
Why might you see an image in the mirror?
When you look in the mirror, you might see someone who looks just like you behind the mirror. There is an image in the mirror.
Light travels in straight lines. The brain uses this fact to work out where the light appears to be coming from. This is where you see the image. It is a virtual image because light has not travelled from it to the eye. You can see how this works in Figure 2.
Figure 2You can see an image in a mirror.
When something is reflected in a flat, or plane, mirror the image is:
- the same shape and size as the real object
- as far behind the mirror as the real object is in front of the mirror.
Left and right appear swapped (changed positions), but the mirror is actually swapping back and front.
A If you stand 1 m in front of a mirror, looking directly at it, how far are you from your image?
What is the law of reflection?
You know that you need light to be reflected off an object for you to see it. Light reflects off a mirror in the same way that a wave reflects off a barrier, or a sound wave reflects off a building.
There is an imaginary line at an angle of 90° to the mirror. This is called the normal. You measure angles from the normal to the rays of light. You can see how to do this in Figure 3.
Figure 3Light is reflected at equal angles. Full text alternative to the content
The angle between the incident ray (the ray coming in) and the normal is the angle of incidence. The angle between the normal and the reflected ray (the ray coming out) is the angle of reflection.
When light is reflected off a mirror, the angle of incidence is equal to the angle of reflection. This is the law of reflection.
B If the angle of incidence is 30o, what is the angle of reflection?
How does light reflect off rough surfaces?
Every surface reflects at least some light. Figure 4 shows how light is reflected off two different surfaces. You can only see your image in surfaces that reflect light in a regular way.
To form an image, the rays from each part of the object have to reflect off a surface in the same way (see Figure 4a). If two rays that are parallel are reflected off a surface at different angles, you won’t see an image (see Figure 4b).
Figure 4You can only see an image in a smooth surface. Full text alternative to the content
C State the type of reflection when light hits a shiny metal pan.
Working scientifically A student wants to investigate the light that is reflected off different types of material using a light meter. Explain why they should repeat the experiment a few times. Decide what type of graph they should use to plot the results.
Stretch zone
- Copy and complete the sentences. When an object is reflected in a mirror, a real/virtual image appears. The image is a different/the same size and distance from the mirror as the real object. If the object moves to the left, the image appears to move to the left/right. The image is formed because light reflects off the mirror so that the angle of incidence/normal is equal to the angle of incidence/reflection.
- Explain why no image is created by objects facing a white wall, even though most of the light hitting it is reflected.
Stretch zone
- Design a model to show how light can be diffusely reflected but still obey the law of reflection. Use marbles and card instead of light and a mirror in your model. Explain how it works.