2. Light and Pinhole Cameras GHB 2005 Pinhole cameras are important because they demonstrate that light travels in straight lines

3. Light bounces off Homer Light enters the eye of an observer Light is produced by a luminous object How can we see Homer Simpson?

4. If light bounces off Homer in only one direction… …Homer can only be seen from one direction This observer can see Homer This observer receives no light from Homer so cannot see him Why can we see Homer from any direction?

5. When light hits a rough surface, it is scattered in many directions, so… … objects can be seen from many directions.

6. What is a pinhole camera? Sealed box with non-reflective coating inside (preferably black) Very small hole (pin hole!) Translucent screen (e.g. tracing paper) When the camera is pointed towards a bright object, an image of the object appears on the screen

7. How does a pinhole camera work? Every point on Homer’s head will scatter light in many directions, however… … only one ray of light from each point on Homer’s head is travelling in precisely the right direction to pass through the pinhole

8. Also… … only one ray from each point on Homer’s foot will be travelling in precisely the right direction to enter the pinhole Light is scattered as it passes through the translucent screen, so…

9. Image is inverted … we see an image on the screen Light scattered by screen Object

10. Drawing ray diagrams for pinhole cameras Ray diagrams show the path of rays of light from an object. They can be tricky to draw, so the best thing is to… CHEAT!!!

11. … so that the rays cross in the pinhole Step 1: Draw your object Step 3: Draw in rays from top and bottom of your object Step 4: Draw in rest of pinhole camera … Step 2: Draw your inverted image and your translucent screen

12. Rules for drawing Ray Diagrams 4. Light always reflects off an object at the same point that it hits the object. 5. When using a diagram to explain how somebody sees something – show the ray of light entering the eye 2. Always use an arrow head to show which direction the rays of light are travelling in 1. Always use a ruler – light travels in straight lines 3. Rays of light should touch the objects that they are reflecting off.