Physics
Lab 3.4 Shadows
Overview
The purpose of this
laboratory class is to show how the size of a source of
light affects the shadow created by an obstruction
between the source and the shadow.
Experiment
Use different sized light
sources to create shadows of an object on a screen.
Observe the effect that the size of the light source and
the distance between the object and the source have on
the nature of the shadow.
Experiment
: Umbra and Penumbra
Equipment
Flashlight with very small
bulb
Light box (Light bulb in
box with an opening in one side – opening should be
about 4 cm2)
Screen (piece of white
paper or board – mounted vertically)
Object to create shadow (pencil
or golf ball)
Procedure
- Arrange the light box
and screen so that an area with the same shape as
the opening in the light box is brightly
illuminated on the screen.
- Measure the distance
between the source and the screen. Measure the
size of the opening in the light box and the size
of the brightly illuminated area on the screen.
- Place the object
between the source and the screen to create a
shadow.
- Move the object
closer to – and further from the source and
observe the nature of the shadow created by the
object
- Select a position
where the umbra and penumbra are clearly visible.
- Measure the distance
of the object from the screen, the size of the
object and the sizes of the umbra and penumbra.
- Draw a ray diagram
showing the sizes of the umbra and penumbra in
relation to the sizes of the object and the light
source.
- The light from the
light box may be regarded as an extended source.
- Remove the reflecting
enclosure from the flashlight to expose the small
bulb.
- Remove the light bulb
from the light box and place the flashlight
inside the box.
- Note the sharpness of
the shadow created by the point source (flashlight
bulb) compared with the shadow using extended
source.
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