You cannot see in the dark, but if the light is turned on suddenly, you can see. Your eyes are still basically the same as before the light came on. Why can you now see?
Eyes are like living optical gadgets. They use light, and they form pictures.
How are 'light' and 'seeing' related? Discuss the following.
What gives off light?
Make a list of objects that give off (emit) light. Try for about 12 things. Put the names of the objects in a table like the one shown. Then you can answer the questions by putting ticks in the columns across the table.
Which objects that produce light have been invented during the last 50 years? Perhaps ask some older people (teachers or parents).
Which of the objects in your list use heat to produce light (ie they are very hot)?
Which objects use electrical energy (or electricity) to produce light?
Which of these objects use stored chemical energy to produce light?
Light and seeing
Light may come directly from the object that produces the light to your eyes, or it may bounce off another object before coming to your eyes. Use this idea to explain the following situations.
Use the information in the diagram with the butterfly to explain how the cat can be seen in the other diagram.
If you look at the light globe, explain how it can be seen.
Challenge
Apart from our eyes, name some other devices that can detect light coming from a light source.
Which animals cannot detect light? (ie they cannot see.)
What evidence is there that plants can detect light?
Cats can see in total darkness? True or false?
What is the connection between rabbits, carrots and good eyesight?
How many eyes do spiders have? What about insects?
The purpose of this activity is to introduce the notion of seeing:
the sources of light
ways of detecting light
transmission of light from the source to the eye
how non-luminous objects are seen.
It is designed to elicit and activate prior knowledge, rather than to make sure the ideas are right.
This activity can be carried out as a whole-class discussion or brainstorm. If time is short, each group could discuss or brainstorm the answers to one of the three sets of questions and report their ideas to the class. There is no right or wrong answer to many of these points, only the opportunity for good discussion.
This activity could be started in class and then finished as a home activity.
If the students do this activity by themselves or in groups, a class discussion at the end of the section would be of value.
Have a range of light sources available for demonstration, such as a candle, light globe, TV screen and LED.
Do not worry if students don't know the answers to some of these questions. They are purely for discussion. For the same reason, there are no right or wrong answers to many of these points, only the opportunity for good discussion.
Some students may be able to go away and find the answers for the class.
Only give the challenge questions to those students who find the other questions too basic.
Either give students specific references to textbooks or other books you know to be in the library or ask them to show their general research skills in the library or on the Internet.
