Key learning points

1. Convex lenses can produce an inverted image on a screen by refracting light.
2. Rays parallel to the principal axis are refracted to the principal focus, located at the focal length of a convex lens.
3. The image distance and size (magnification) depend on the power of the lens and the object distance.
4. As the object distance decreases, the image distance and size both increase, until the object reaches the focal length.
5. If the object is too close to the lens, the rays leaving the lens are parallel/diverging, images can't form on a screen.

Keywords

• Diminished - Diminished means smaller than an object’s real size. It is the opposite of magnified.

• Convex - A convex shape bulges ‘out’ rather than bulging ‘in’ (concave).

• Principal focus - Rays of light incident on a convex lens parallel to the principal axis are focused to a point called the principal focus.

• Focal length - The focal length is the distance from the centre of the lens to the principal focus.

• Lens power - The greater the power of a lens, the greater the angles through which light is refracted and the shorter the focal length.

Common misconception