1. Lenses
There are two different types of lenses.
Convex lens Concave Lens
Copy the diagram of each lens into your book.
You should have an example of each type of lens, look
through each lens at objects that are close and far away.
Record what you see in your book. How does this
change if the lens is moved away from the eye?

2. Lenses
Convex lenses are also known as
converging lenses
Concave lenses are also known as diverging lens
To find out why you need to collect some equipment.
A ray box, a power supply, a sheet of plain paper and two
lenses. Your teacher will show you how to work the
power supply.
Start with the convex lens.

3. Lenses
Place the lens in the centre of the paper. Use the ray
box to produce 3 parallel rays of light which hit the
lens. Make sure one of them hits the centre of the
lens.
What happens to the rays
Incident rays when they pass through
the lens?
Produce a good diagram of
what you see in your books
and explain why concave
lenses are also called
converging lenses.

4. Lenses
This is what you should have seen.
Principal focus
Incident rays
(parallel)
F
f
(focal length)
Did you notice that the light rays bend on entering the lens and leaving the
lens?
Make sure you know what the princpal focus is and how this allows us to
measure the focal length.
What was the focal length of your lens?

5. Lenses
Incident rays of light are parallel
Principal focus
Another convex Lens

6. Lenses
Concave Lens – know do the same for the convex lens
What happens to the rays
when they pass through
Incident rays
(parallel) the lens?
Produce a good diagram of
what you see in your books
and explain why concave
lenses are also called
diverging lenses.

7. Lenses
The light rays are spread
out or DIVERGED by this
lens.
Incident rays
(parallel) Parallel rays are diverged
F
so that they appear to come
from the principal focus (F)
of the concave lens.
Objects always look smaller
through a concave lens.
f
(focal length)
Did you notice that the light rays bend on entering the lens and leaving the lens?
Make sure you know what the principal focus and focal length are for a concave
lens.
Can you think of a way of measuring the focal length
of your diverging lens? (Hint it involves drawing)l

8. Lenses
Incident rays are parallel
Rays leaving the lens are diverging
The black lines show where the diverging light appears
to have come from the Prinicpal Focus

9. Lenses
Forming Images
Screen
The rays of light from the car are converged by the lens, to form an image on
the screen.
The image is inverted (upside down)
and real (the rays of light pass through the lens and an image is
formed on the screen)
and diminished (smaller than the object).

10. Lenses
Cameras
Film/screen
Object
In a camera the image is
smaller than the object we Image: Real, Inverted and
say the image is diminished diminished

11. Lenses
Insert photograph here
Projectors
The image is inverted, real (its on a screen ) and
magnified (larger than the object)
Magnification = height of image
height of object

12. Lenses
Question 1. – Copy out and complete the following
a) A convex lens _____ rays of light, but a concave lens _____
rays of light.
b) Parallel rays of light are refracted by a convex lens to a
point called the _____ ____.
The focal length is the distance from the _____ _____ to the
_____ of the lens.
c) A fat convex lens is a _____ lens, with a _____ focal length.
d) A real image can be formed on a _______
e) The image in a concave lens is always _______ than the
______.
Centre, converges, diverges, focus, object, Answer
principal, screen, short, smaller, strong

13. Lenses
Question 1. – Copy out and complete the following
a) A convex lens converges rays of light, but a concave lens
diverges rays of light.
b) Parallel rays of light are refracted by a convex lens to a
point called the principal focus.
The focal length is the distance from the principal focus to
the center of the lens.
c) A fat convex lens is a strong lens, with a short focal length.
d) A real image can be formed on a screen.
e) The image in a concave lens is always smaller than the
object.
Got something wrong ask your teacher!!

14. Lenses
Question 2 – copy and complete the ray diagrams
A B
C D
F
Answer

15. Lenses
Question 2 - answers
A B
C D
F
Did you remember to show the light bending on
entering and leaving the lens?
Got something wrong ask your teacher!!

16. Lenses
Insert picture here
That’s all for now folks
but
You need to check through the
work from today at home
Next lesson: you will be using
what you have learnt today to
predict the size and position of an
image and then checking your
prediction.