Thin Converging Lenses 1
Physics: Cambridge International GCSE Supplement, topic 3.3.1
Thin Converging Lenses
A thin converging lens (curved piece of glass) causes parallel rays of light that pass through it to converge (come together).
Refraction
- When a beam of light strikes a thin converging lens, the light is refracted twice:
- Once towards the normal (90 degrees to the lens) as the light enters the lens;
- And once away from the normal (90 degrees to the lens) as the light leaves the lens.
- Note: It is assumed that the lens is very thin to only consider one reflection at the optical axis.
- When you see ray diagrams the lens will be represented by a single line.
Optical axis
- The optical axis is the line perpendicular to the principal axis and passing through the optical centre (lens’ centre).
- It is used to show the position of the lens.
Principal focus
- Light rays that are parallel to the optical axis pass through the lens and converge (come together) at the principal focus.
- There is one principal focus on each side of the lens as light can pass through the lens in either direction.
Focal length
- The focal length is the distance from the centre of the lens to the principal focus.
Test yourself on Thin Converging Lenses 1
What is the angle between the optical axis of a lens and its face?
Which of statements are true of a thin converging lens?