Physics 3 - Light and Sound - Using Lenses

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Using Lenses

The position and nature of the image formed by a lens depends on:

- The focal length of the lens

- The distance form the object to the lens

If we know the focal length and the object distance, we can find the position and nature of the image by drawing a ray diagram.

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Using Lenses 2

In a camera, an converging lens is used to produce a real image of an object on a film (or an array of pixles in the case of a digital camera). The position of the lens is adjusted to focus the image on the film, according to how far away the object is.

- For a distant object, the distance from the lens to the film must be equal to the focal length of the lens.

- The nearer an object is to the lens, the greater the distance from the lens to the film.

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Using Lenses 3

Formation of a virtual image by a converging lens:

The object must be between the lens and its principal focus. The image is formed on the same side of the lens as the object.

The image is virtual, upright and larger than the object. It can only be seen by looking through the lens. This is how a magnifying glass works.

Formation of a virtual image by a diverging lens:

The image formed by a diverging lens is always virtual, upright and smaller than the object.

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