Lenses and images
Different lenses produce different kinds of energy.
Lenses form images by refracting light and changing its direction.
Converging and diverging lenses are the main two types of lense.
A converging lens is convex - it bulges outwards. It causes parallel rays of light to converge (move together) at the prinicpal focus.
A diverging lens is concave - it caves inwards. It causes parallel rays of light to diverge (spread out).
The axis of the lense is a line passing through the middle of the lens.
The prinicpal focus of a converging lens is where rays hitting the lense parallel to the axis will meet. The principal focus of a diverging lens is the point where rays hitting parallel to the axis appear to all come from. You can trace them back until they all meet up.
The distance from the centre of the lens to the principal focus is called the focal length.
Lenses and images - 3 rules for converging and div
Refraction in a converging lens has 3 rules.
- An incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side.
- An incident ray passing through the principal focus refracts through the lens and travels arallel to the axis.
- An incident ray passes through the centre of the lens carries on in the same direction.
Refraction in a diverging lens also has 3 rules.
- An incident ray parallel to the axis refracts through the lens and travels in line with the prinipal focus.
- An incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis.
- An incident ray passing through the centre of the lens carries on in the same direction.
Lenses and images - real and virtual images
A real image is light from an object comes together to form an image on a 'screen'.
A virtual image is when the rays are diverging, so the light from the object appears to be coming from a comletely different place.
When you look in a mirror, you see a virtual image as the face appears to be behind the mirror.
You get a virtual image when looking at an object through a magnifying lens because the virtual image looks bigger than the object actually is.