Lenses can form images of the objects placed in front of them. Images can be described as:
● Real – The light rays converge and meet each other at a point, which means that the Image can be projected onto a screen.
● Virtual – The light rays diverge away from a point, so the light rays do not meet. However, they appear to meet behind the lens. Virtual Images can not be projected onto a screen.
● Magnified – The image formed is larger than the object
● Diminished – The image formed is smaller than the object
● Upright – The image formed is the same way up as the object
● Inverted – The image formed is upside down compared to the object – Real images are always inverted
We can use ray diagrams to understand how lenses work and to identify the location of the image formed.
In a ray diagram, a convex lens is drawn as a vertical line with arrows pointing outwards in both directions. This is to resemble the shape of a convex lens.
Whereas, a concave lens is drawn as a vertical line with arrows pointing inwards. This is to resemble the shape of a concave lens.
1. Draw a line from the top of the object, parallel to the axis. Once the line reaches the lens, refract it through the focal point.
2. Draw a line through the focal point before the lens. Once it reaches the lens, refract the ray parallel to the axis.
3. Draw a line from the top of the object, through the centre of the lens.
If an object is placed at a greater distance than the focal length from the lens, then the convex lens will produce a real image. However, the convex lens will produce a virtual image if the image is placed closer to the lens than the focal length.
Both cameras and eyes have convex lenses. Below is the ray diagram for a distant object which is greater than twice the focal length from the lens.
The image is:
A magnifying glass is a convex lens that produces an enlarged image. In this case, the object is less than the focal length from the lens. Below is the ray diagram for a magnifying glass.
The image is:
Concave lenses always produce images that are:
Below is an example of a ray diagram for a concave lens.