Lenses
A lens is a curved piece of transparent material that refracts light to focus it or spread it out.
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A lens is a curved piece of transparent material that refracts light to focus it or spread it out.
- Convex lenses converge light
- Concave lenses diverge light
- The focal length is the distance to the focus
🧠 Quick quiz
Three questions. Score 2 or more to complete the topic.
What is Lenses?
Within Physics, which covers forces, energy, waves, electricity, magnetism, light and space explained through motion and experiments, this topic explains Lenses. Physics topics explain how things move, push, heat up and carry energy, so each one here pairs a definition with a live model you can change.
Check that you can explain Lenses in your own words and give one example from everyday life. If you can do that, you have understood the core idea.
Understanding Lenses explains how the physical world behaves, from sport and transport to electricity and medicine.
Lenses in detail
A lens refracts light to form images. A converging (convex) lens brings parallel rays to a focus at its principal focus, at a distance equal to the focal length. A diverging (concave) lens spreads rays so they appear to come from a virtual focus.
Ray diagrams use three rays: one parallel to the axis, one through the centre and one through the focus. The image can be real or virtual, upright or inverted, magnified or diminished depending on the object distance. Magnification = image height ÷ object height. Lenses are used in cameras, spectacles, magnifying glasses, microscopes and telescopes.
How the interactive helps you understand Lenses
Watch the light rays in the interactive. Use any sliders or buttons it offers to change the values and see how the light rays responds.
Before you change anything, predict the result. Then change one value at a time and check whether your prediction was right. This is a quick way to build a correct mental model of Lenses.
Real-life uses and examples
- Predict what a ball, car or circuit will do with Lenses before you do the calculation.
- Explain everyday devices, such as brakes, lifts or chargers, using Lenses.
- Use Lenses to make sense of a practical and its results.
Common mistakes to avoid
- Mixing up Lenses with a related quantity that has different units.
- Forgetting that some quantities, such as force or velocity, also have a direction.
- Learning the definition without testing it. Use the quiz and the interactive to check that you can apply the idea.
Frequently asked questions about Lenses
What is Lenses?
A lens is a curved piece of transparent material that refracts light to focus it or spread it out.
What are the most important points about Lenses?
The main points are: Convex lenses converge light; Concave lenses diverge light; The focal length is the distance to the focus.
Why is Lenses useful?
Understanding Lenses explains how the physical world behaves, from sport and transport to electricity and medicine.
How can I practise Lenses?
Open the interactive at the top of this page and change the controls one at a time. Predict the result before each change, then take the three-question quiz. A score of two or more marks the topic as complete on this device.
Which topics are related to Lenses?
Related topics in Physics include Electromagnetic Spectrum, Electric Current, Series and Parallel Circuits.