Yr9GCSE2016
Lenses and Vision
Lenses
●A lens forms an image by refracting light.
●In a convex or converging lens, parallel rays of light are brought to a focus at the principal focus. The distance from the lens to
the principal focus is called the focal length.
●The nature of an image is defined by its size relative to the object, whether it is upright or inverted relative to the object and
whether it is real or virtual.
●The focal length of a lens is determined by:
■ the refractive index of the material from which the lens is made, and
■ the curvature of the two surfaces of the lens.
Ray Diagrams
●The nature of the image produced by a converging lens for an object placed at different distances from the lens.
●In ray diagrams a convex lens will be represented by: A concave lens will be represented by:
●The use of a converging lens as a magnifying glass.
●The nature of the image produced by a concave or diverging lens.
●The construction of ray diagrams to show the formation of images by converging and diverging lenses. Candidates may be asked
to complete ray diagrams drawn on graph paper.
●The magnification produced by a lens is calculated using the equation:
image height
magnification=
object height
●Draw and interpret ray diagrams in order to determine the nature of the image.
The Eye
●The structure of the eye. The structure of the eye is limited to:
■ retina
■ lens
■ cornea
■ pupil /iris
Candidates should know the function of these named parts. Candidates should understand how the action of the ciliary muscle
causes changes in the shape of the lens, which allows the light to be focused at varying distances.
●Range of vision. The eye can focus on objects between the near point and the far point. Candidates should know that the near
point is approximately 25 cm and the far point is infinity.
●Comparison between the structure of the eye and the camera. Candidates should be aware that the film in a camera or the CCDs
in a digital camera is the equivalent of the retina in the eye.
Correcting Vision
●Correction of vision using convex and concave lenses to produce an image on the retina:
■ long sight, caused by the eyeball being too short, or the eye lens being unable to focus
■ short sight, caused by the eyeball being too long, or the eye lens being unable to focus.
●The power of a lens is given by:
1
𝑃=
𝑓
P is power in dioptres, D
fis focal length in metres, m
Candidates should know that the power of a converging lens is positive and the power of a diverging lens is negative.
●For a given focal length, the greater the refractive index, the flatter the lens. This means that the lens can be manufactured
thinner.
●Evaluate the use of different lenses for the correction of defects of vision.
What does ‘refract’ mean? __________________________________________________________________________________
When does it happen? _____________________________________________________________________________________
Yr9GCSE2016
________________________________________________________________________________________________________
Lenses refract light and have many uses. List some of these uses.
________________________________________________________________________________________________________
________________________________________________________________________________________________________
When dealing with light and lenses it is important to use the correct vocabulary. Explain what the following words mean when used
to describe an image produced through a lens.
Inverted _________________________________________________________________________________________________
Upright __________________________________________________________________________________________________
Magnified ________________________________________________________________________________________________
Diminished ______________________________________________________________________________________________
Real ____________________________________________________________________________________________________
Virtual __________________________________________________________________________________________________
Complete the above diagrams by labelling each type of lens and drawing what happens to the parallel rays of light after they have
reached the lens. You may wish to add annotations to the diagrams.
What is meant by the term ‘focal point’? ________________________________________________________________________
________________________________________________________________________________________________________
What is meant by the term ‘focal length’? _______________________________________________________________________
________________________________________________________________________________________________________
What two factors will affect the focal length of a lens?
________________________________________________________________________________________________________
________________________________________________________________________________________________________
Yr9GCSE2016
Ray Diagrams
Look at another different objects through a convex lens. Describe how they appear (compared to normal) when:
A) You hold the lens near to your eye and look at an object that is a few centimetres away.
________________________________________________________________________________________________________
________________________________________________________________________________________________________
B) You hold the lens near to your eye and look at an object that is a few metres away.
________________________________________________________________________________________________________
________________________________________________________________________________________________________
Now using a concave lens, describe how they appear when:
C) You hold the lens near to your eye and look at an object that is a few centimetres away.
________________________________________________________________________________________________________
________________________________________________________________________________________________________
D) You hold the lens near to your eye and look at an object that is a few metres away.
________________________________________________________________________________________________________
________________________________________________________________________________________________________
When drawing ray diagrams how are the two types of lenses represented?
Converging
lens
Diverging
lens
To complete the ray diagram showing the formation of images using a converging lens follow these steps:
1. Draw a line from the _____________________________________________________________________________________
2. Continue this line ________________________________________________________________________________________
3. Draw a line from the _____________________________________________________________________________________
4. The image is formed where ________________________________________________________________________________
To complete the ray diagram showing the formation of images using a diverging lens follow these steps:
1. Draw a line from the _____________________________________________________________________________________
2. Continue this line ________________________________________________________________________________________
3. Draw a line from the _____________________________________________________________________________________
4. The image is formed where ________________________________________________________________________________
Complete this ray diagram to show how the lens produces an image of the object.
Yr9GCSE2016
State three words to describe the nature of the image produced by the lens.
1______________________________ 2______________________________ 3______________________________
Complete this ray diagram to show how the lens produces an image of the object.
F
O
L
F
Eye
State three words to describe the nature of the image produced by the lens.
1______________________________ 2______________________________ 3______________________________
Yr9GCSE2016
Complete this ray diagram to show how the lens produces an image of the object.
Object
F
Eye
Diverging lens
State three words to describe the nature of the image produced by the lens.
1______________________________ 2______________________________ 3______________________________
The Eye
Here is a diagram of the eye, label the different parts.
Explain the function of the different parts of the eye.
Retina __________________________________________________________________________________________________
Lens ___________________________________________________________________________________________________
Cornea _________________________________________________________________________________________________
Pupil _____________________________________________________________________________________________
Iris_____________________________________________________________________________________________________
Yr9GCSE2016
Correcting Vision
Each of our eyes has a lens that can change shape to focus on near and far objects. Complete the diagrams to show rays of light
from near and far objects focused onto the retina (at the back of the eye). This would be described as normal vision.
Near objects
Far objects
Some people are ‘short sighted’. Explain what this means and complete ray diagrams to demonstrate this.
________________________________________________________________________________________________________
________________________________________________________________________________________________________
Near objects
Far objects
Some people are ‘long sighted’. Explain what this means and complete ray diagrams to demonstrate this.
________________________________________________________________________________________________________
________________________________________________________________________________________________________
Near objects
Far objects
Explain how short sightedness is corrected. You should include which type of lens is used and a ray diagram like those before.
________________________________________________________________________________________________________
________________________________________________________________________________________________________