|Small torches or small incandescent bulbs, Small cardboard squares that are a few cm on each side (to cast the shadow), Retort stands to hold the torch, White sheet to use as a screen|
|Suggestions for use:|
The students begin by drawing the arrangement of apparatus they would require to observe a shadow on a screen. They then qualitatively investigate the formation of shadows in an attempt to deduce what parameters affect its size, with the teacher guiding them towards providing answers to the following questions:
1. If the projection screen and torch are fixed in place, how does the size of the shadow change as the cardboard square is moved towards or away from the torch?
2. If the torch and cardboard square are fixed in place, how does the size of the shadow change as the projection screen is moved towards or away from the cardboard square?
3. If the screen and cardboard square are fixed in place, how would the size of the shadow change as the torch is moved towards or away from the cardboard square?
The challenge for the students is then to try and explain their observations based on what they know about the propagation properties of light.
|If I place a green bottle in front of the bulb, I see a green ‘silhouette’ cast on the wall. This grows in size and decreases in size depending on the bottle’s distance from the screen and torch. Is this also a shadow?