Images (Cambridge International IGCSE Science)

Characteristics of images

• An image can be described using the following characteristics which compare it to the object:

  • Enlarged/same size/diminished
  • Upright/inverted

• An image viewed through a magnifying glass is:

  • Enlarged, bigger than the object
  • Upright, has the same orientation as the object

An image viewed through a magnifying glass

An image viewed through a magnifying glass is enlarged and upright compared to the object

• An image viewed through an eye, a camera, or a glasses lens is:

  • Diminished, smaller than the object
  • Inverted, upside down compared to the object

An image viewed by the eye

An image viewed by the eye is diminished and inverted compared to the object

Converging lens - real image

Interpreting converging ray diagrams

• The three main rules for interpreting ray diagrams are as follows:

1. Rays that pass through the optical centre of the lens travel straight through, without changing direction

1. Rays that are parallel to the principal axis will be refracted and pass through the focal point f

3. Rays passing through the focal point f will emerge parallel to the principal axis

Interpreting converging ray diagrams of real images

• The position of the object relative to the focal length of a converging lens affects the position, size, and orientation of the image formed

• For real images formed by a converging lens, there are three common object positions to consider:

  • the object is placed further than 2f from the lens
  • the object is placed at 2f from the lens
  • the object is placed between f and 2f from the lens

Interpreting a ray diagram for an object placed further than 2f

• The image that forms will have the following properties:

Interpreting a ray diagram for an object placed at 2f

• The image that forms will have the following properties:

Interpreting a ray diagram for an object placed between f and 2f

• The image that forms will have the following properties:

Worked Example The ray diagram below shows a real image formed by a converging lens.

Describe the image formed by the lens.

Answer:

• The image is:

  • Formed between f and 2f from the lens
  • Real
  • Inverted
  • Diminished