Convex and concave lenses

Convex and concave lenses

Pencil and paper
Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
Working with Students
This task is about how concave and convex lenses work.

Two types of lenses are concave and convex.  
a)
Predict what you think will happen when each lens is held about 5cm above a pencil as illustrated in the diagram below.
 
Prediction:  
 
Convex lens:
 
 
 
 
Concave lens:
 
 
 
 
 

 

      
b)
Now collect the lenses and try this out. Draw your results on the diagrams above.
 
c)
In terms of light rays, explain what happens for each lens.
 
  Convex lens:
 
 
 
 
  Concave lens:
 
 
 
 
 
d)
Name or describe a practical situation where each lens could be used.
 
  Convex lens:
 
 
  Concave lens:
 
Task administration: 
Equipment:
Pencil; concave lens; convex lens.
Lenses are given to student after they have completed part a).
Level:
5
Curriculum info: 
Science, Investigating in science, Physical World
Keywords: 
physics concepts, energy, light, lenses
Description of task: 
Students predict and investigate the way in which a concave and a convex lens distort the image of a pencil.
Curriculum Links: 
Science capabilities
The capabilities focus is brought about by the conversations you have and the questions you ask.
 
Capability: Interpret representations
This resource provides opportunities to discuss particular science representations e.g., light ray diagrams. 
 
Capability: Gather and interpret data
This resource provides opportunities to discuss the methodology used in lens investigations.
Science capabilities: 
Gather and interpret data, Interpret representations
Answers/responses: 

a)

  

Any prediction.

b)

  
Convex lens

 Concave lens

c)

  

Convex lens: The light rays that go through a convex lens are brought to a focus.
Concave lens: The light rays that go through a concave lens are diverged.

d)

i)

 

 

 

 

ii)

Convex

Any 1 of:

  • To magnify an object.
  • Lenses used in glasses for someone who is long-sighted.
  • To focus light rays to ‘start’ a fire.
  • Other acceptable answers.

Concave

Any 1 of:

  • Lenses used in glasses for someone who is short-sighted.
  • Other acceptable answers.
Next steps: 
Extension
Students could do a drawing to show light rays travelling through a lens.