Science - How can I explain that light travels in straight lines?

The key learning points to this lesson was to understand that light travels in straight lines, and  know the light travels out from a source of light in all directions.

The children set up 4 pieces of card with holes in the middle of 3 of them. 

They lined up the cards in a straight line. 

We dimmed the lights of the classroom and switched on torches opposite the first piece of card. 

The children were able to observe what happened to the light of the torch when all cards were lined up correctly, They were able to discuss the reason for this and what it explained about travelling light.