Virtual Images (Cambridge (CIE) IGCSE Physics)
Revision Note
Written by: Katie M
Reviewed by: Caroline Carroll
Converging lens - virtual image
Extended tier only
Constructing converging ray diagrams of virtual images
A single lens placed at a distance less than the focal length of an object can be used as a magnifying glass
A converging lens ray diagram for an object placed less than f
Ray diagram showing light converging through a magnifying glass to form a magnified virtual image
The image that forms will have the following properties:
The image forms... | at 2f (on the same side as the object) |
The nature of the image is... | virtual |
The orientation of the image is... | upright |
The size of the image is... | magnified |
Diverging lens - virtual image
Image formation by a diverging lens
No matter the position of the object all images formed by diverging lenses are:
Virtual (and not real)
Upright (the same as the object)
Diminished (smaller than the object)
On the same side of the lens as the object
For an object placed at any distance away from the lens (further than the focal point or closer than):
The ray of light incident on the centre of the lens does not change direction
The rays of light parallel to the principal axis are refracted
These rays can be extrapolated backwards
It appears that they come from a virtual focus
A visible projection cannot be formed on a screen
Virtual image produced by a diverging lens with object beyond f
A diverging lens always produces a virtual image no matter the position of the object in relation to the focal point or the lens. Here the object is further away from the lens than the focal point.
Virtual image produced by a diverging lens with object closer than f
A diverging lens always produces a virtual image no matter the position of the object in relation to the focal point or the lens. Here the object is closer to the lens than the focal point.
Comparing converging & diverging lenses
The image produced by a converging lens can be either real or virtual
This means the image can be inverted (real) or upright (virtual)
The image produced by a diverging lens is always virtual
This means the image will always be upright
Worked Example
An object is placed outside the focal point of a diverging lens.
Complete the ray diagram by drawing where the image of this object will be seen.
Answer:
Step 1: Draw a line from the top of the object through the middle of the lens
The top of the image lies somewhere along this line
Step 2: Draw a line from the focal point through the top of the lens
The dashed line shows the continuation of the upward arrow
The top of the image is where the two lines cross
Examiner Tips and Tricks
You are not expected to draw ray diagrams for a diverging lens but you must be able to explain how the virtual images are formed.
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