Refraction in a lens occurs when light bends as it passes from one medium (like air) into another medium (like glass or plastic) and then out again.
Understanding Lens Refraction
A lens is designed to manipulate light using refraction. Here’s how it works:
- Entering the Lens: When light rays travel from air and hit the curved surface of the lens, they slow down and change direction. This bending is refraction.
- Shape Matters: The specific way light refracts depends on the shape of the lens.
- Concave lenses are thinner in the middle and thicker at the edges, causing parallel light rays entering the lens to refract outwards, or spread out.
- Convex lenses are thicker in the middle and thinner at the edges, causing parallel light rays entering the lens to converge (come together) at a point called the focal point.
- Double Refraction: Light rays refract twice when passing through a lens:
- First, when they enter the lens.
- Second, when they leave the lens and re-enter the air.
- Center Light Rays: Only the light rays that pass through the exact center of a lens remain straight and do not refract.
How a Lens Forms an Image
The combined effect of refraction across the lens focuses or disperses light, enabling it to form an image. Here is an outline:
- Converging lenses (convex) focus light rays onto a focal point, which can be used to create a real image (an image that can be projected onto a screen) that is either enlarged, reduced, or the same size as the object depending on the lens's focal length and the object's distance. These are commonly used in cameras, telescopes, and eyeglasses for farsightedness.
- Diverging lenses (concave) spread light rays out, making objects appear smaller and usually forming a virtual image (an image that cannot be projected). These are used for correcting nearsightedness.
Refraction in Lenses - Key Points
| Feature | Description |
|---|---|
| Refraction | Bending of light as it passes from one medium to another. |
| Lens Shape | Dictates how light will refract. |
| Concave Lens | Light rays diverge/spread out (used to correct nearsightedness) |
| Convex Lens | Light rays converge/come together (used to correct farsightedness) |
| Double Refraction | Light refracts twice, entering and exiting the lens. |
| Central Light Rays | These rays pass straight through the center of the lens without refraction |
