All shadows are created equal, are not they? Hold your hand several inches above this book. Raise and lower your hand while you observe your shadow. Does the appearance of the shadow change? If so, how? When is the shadow sharpest? When is it darkest?
Things Required:
Scrap paper, Carbon paper, Pair of scissors,
Torch, Wax paper, Rubber band
Directions:
Place a sheet of scrap paper beneath the weird drawing on the next page. Then, insert a sheet of carbon paper (copying side down) between the page and the scrap. Trace out the odd outline.
Use a pair of scissors to cut out carefully the three irregular dark shapes of the carbon copy.
As in the previous experiment, cover the lens of a torch with an unwrinkled, double thickness of wax paper. Pull the wax paper tight and secure this covering with a rubber band.
Hold the cutout about 2 inches away from the wall. Aim the beam of the torch at the cutout. What do you see? Are the edges of the image sharp or “soft”? How many shades can you distinguish in this shadow?
Slowly, move the scrap paper away from the wall. What happens to the shadow? Keep the paper stationary and continue moving the torch back. What happens now?
This Is What Happens:
When the shadow mask is held close to the wall, a dark and sharp shadow is cast. People in science call this well-defined shadow an umbra. If you were the size of an ant and walked into this umbra, you wouldn’t see the torch beam. It would be completely dark (except for the other light that was in the room).
As the shadow mask is moved away from the wall, the lighter shades of shadow appear. These lighter shades form the penumbra of the shadow.
The penumbra isn’t in complete darkness. This time, our ant-sized visitor would see a part of the torch beam.
