Lenses

Question 1

What is a converging lens and what does it cause light to do?

Answer 1

A lens which is convex and causes rays of light to bend towards each other.

Question 2

What are rays parallel/non-parallel to the principle axis called?

Answer 2

Axial/non-axial rays.

Question 3

What is the point at which axial rays passing through a converging lens called?

Answer 3

The principle focus.

Question 4

Where do non-axial rays converge when passed through a converging lens?

Answer 4

At a point on the focal plane which is the plane perpendicular to the principle axis.

Question 5

What is the focal length?

Answer 5

The perpendicular distance between the lens axis and the focal plane.

Question 6

How can you use a ray diagram to determine the position of an image?

Answer 6

• Draw axial ray from top of object, and draw line after being refracted through principle focus
• Draw ray through centre of lens which does not get refracted and see where the rays meet

Question 7

What happens if the two rays do not meet on a ray diagram and separate out?

Answer 7

You extend the rays back to where they appear to meet - virtual image formed.

Question 8

What is the lens equation and what does each letter mean?

Answer 8

1/f = 1/u + 1/v
f = focal length
u = distance between object and lens axis
v = distance between image and lens axis