GCSE-ready- Home
- Lessons
- GCSE & IGCSE Physics
- Lenses and colour
Lenses and colour
🎬 The doodle video for this lesson is coming soon. Subscribe on YouTube to see it first.
Lenses bend light to form images. Colour depends on which wavelengths an object reflects. Separate Physics only.
Lenses
A converging (convex) lens brings parallel rays together at the principal focus.
A diverging (concave) lens spreads rays out.
The focal length is the distance from the lens to the principal focus.
Thicker, more curved lenses are more powerful.
A diverging (concave) lens spreads rays out.
The focal length is the distance from the lens to the principal focus.
Thicker, more curved lenses are more powerful.
Colour
White light is a mix of all colours.
An object looks red because it reflects red light and absorbs the others.
A white object reflects all colours; a black object absorbs all colours.
Filters only let their own colour through.
An object looks red because it reflects red light and absorbs the others.
A white object reflects all colours; a black object absorbs all colours.
Filters only let their own colour through.
Specular and diffuse reflection
Specular: from a smooth surface, giving a clear image.
Diffuse: from a rough surface, scattering light in many directions.
Diffuse: from a rough surface, scattering light in many directions.
A blue shirt is seen under red light. What colour does it look?
- The shirt only reflects blue light.
- Red light is absorbed, and there is no blue to reflect.
Answer: Black
Converging lenses bring light to a focus; diverging lenses spread it out. Objects appear the colour they reflect. Smooth surfaces give specular reflection; rough surfaces give diffuse reflection.
Check you have got it
Answer 6 quick questions with instant marking. If you get one wrong, GCSE-ready shows you why and gives you another go. It is free, and you do not need an account.