P3 lenses – Topic 2 - Fact Sheet
Types of lenses
1. What is the name given to a lens that brings light
together to a focal point? [1]
Converging Lens
2. What is the name given to a lens that lens that
spreads light out? [1]
Diverging Lens
3. What is the shape of a lens that makes a diverging
lens? [1]
Concave
4. What is the shape of a lens that makes a
converging lens? [1]
Convex
5. A line drawn with arrows pointing out represents
this type of lens [1]
Concave
6. A line drawn with arrows pointing in represents
this type of lens [1]
Convex
7. This describes how much light is refracted
through a lens [1]
Curvature
8. What is refraction? [1]
When light is bent as it passes
between transparent mediums of
different densities
Lens diagrams and equations
9. What is focal length? [1]
It is the distance from the centre
lens to the focus
10. Principle Focus [1]
The point at which rays of light
meet
11. For parallel rays of light the focal point lies on this
[1]
The principle axis
12. What is the normal line? [1]
A line drawn at 90o to the surface
of an object
13. Explain magnification [1]
The process of enlarging
something in appearance, not in
physical size.
14. How to calculate power of a lens? [1]
Power = 1 / focal length
15. What is the unit used for optical power of a lens?
[1]
Dioptre
16. How do you calculate the refractive index? [1]
sin i / sin r
17. How to calculate magnification? [1]
Image height / object height
Uses of lenses
18. What does virtual image mean? [1]
The image is on the same side as
the object
19. What does real image mean? [1]
The image is on the opposite side
as the object and can be formed
on a screen
20. Give example of an object that forms a virtual
image[1]
Magnifying glass
21. Give example of an object that forms a real image
[1]
Projector or camera
22. Describe the image formed by a camera [3]
Inverted
23. Describe the image formed by a magnifying glass
[3]
Erect
24. Describe the image formed by a projector [3]
Inverted Enlarged
Diminished
Enlarged
Real
Virtual
Real
Eye sight
25. Explain short-sightedness [1]
Light focuses before the retina
26. What is the problem if you are long sighted? [1]
You would have a difficulty of
focussing on objects that are close
to the eye.
27. Explain long-sightedness [1]
Light focuses beyond the retina
28. What does the cornea do? [1]
Refracts light
29. What do the ciliary muscles do? [1]
Controls the shape of the lens, to
enable the eye to focus objects
30. What does the lens do? [1]
Refracts the light on to the retina
31. The greater the refractive index of the glass [1]
The thinner the lens needed for
making lenses for glasses
Skills – Calculations
32. Angle of incidence = 50o
Angle of refraction = 35o
What is the refractive index? [1]
33. Angle of incidence = 30 o
Angle of refraction = 28 o
What is the refractive index? [1]
34. Angle of incidence = 55 o
Refractive index = 1.5
What is the angle of refraction? [1]
35. Angle of refraction = 30 o
Refractive index = 1.2
What is the angle of incidence? [1]
36. If a lens has a power of 2 Dioptre what is the
focal length? [1]
37. If a lens has a power of 5 Dioptre what is the
focal length? [1]
38. If a magnifying glass has a magnification of 2
and the object being viewed is 5cm long, how
long will it appear to be? [1]
39. If a magnifying glass has a magnification of 3
and the object being viewed is 8cm long, how
long will it appear to be? [1]
40. If a magnifying glass is used to view an object
4cm long, makes it appear 12cm long, what is
the magnification? [1]
41. If a magnifying glass is used to view an object
6cm long, makes it appear 24cm long, what is
the magnification? [1]