Lenses (Edexcel GCSE Physics): Revision Notes
📚 Revision Notes
Lenses
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Lenses form images by refracting light and changing its direction. There are two main types of lenses, each with different shapes and opposite effects on light rays:
Two Types of Lenses:
| Effect on Light | Principal Focus | |
|---|---|---|
| Converging Lens (Convex) | Causes parallel rays of light to come together (converge) at the principal focus. | The point where rays hitting the lens parallel to the axis all meet. |
| Diverging Lens (Concave) | Causes parallel rays of light to spread out (diverge) as if they are coming from a focal point behind the lens. | The point where rays hitting the lens parallel to the axis appear to come from (behind the lens). |
Types of Images Formed by Lenses
Images are formed at points where light rays from an object appear to come together.
| Image Type | Description | Example |
|---|---|---|
| Real Image | Formed when light rays actually come together to form an image that can be projected onto a screen. | The image formed on the retina of your eye. |
| Virtual Image | Formed when light rays appear to come from a location different from where they actually are. The rays do not actually meet, so the image cannot be projected onto a screen. | The image seen through a magnifying glass. |
Power of a Lens and Focal Length:
The power of a lens increases with its curvature.
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Focal length is the distance from the lens to the principal focus. A more powerful lens has a shorter focal length.
To make a more powerful lens:
- Use a material that focuses light better.
- Increase the curvature of the lens, as a more curved lens will focus light more strongly, resulting in a shorter focal length.