Why do shadows change shape when light is shone on them?

  • Level: High School 
  • Thread starter danielhaish
  • Start date
  • Tags Tags
    Light
5 replies · 2K views · last reply
danielhaish
Messages
152
Reaction score
10
if you put a light on object you will see shadow in the shape of the object . it would looks like the following picture
Diagram of a black rectangle above a light blue horizontal line, with yellow vertical lines descending from the top and bottom edges, drawn on a white background.

the blue part is the object.
but if you point a laser or light on specific object you will be able to observe it from differences angles like in the following picture
Diagram of a red point source above a light blue horizontal line, with dashed blue rays fanning out to four black ellipse outlines at different positions, each with a small blue line touching it.

the black circles are quemen eyes and the red point is leaser .
so my question is whether the light spreading or not because if it does spread i would expect the shadow shape to looks like that
Diagram of a black rectangular object above a thin blue line, with two yellow lines forming a V-shaped ray path below it, meeting at a point at the bottom.

but if it doesn't the light would return only to one angle
 
Last edited:
danielhaish said:
my question is whether the light spreading or not because if it does spread i would expect the shadow shape to looks like that
Harsh-Light-iPhone-Street-Photos-39.jpg
 
  • Like
Likes   Reactions: danielhaish
Dale said:
Black and white photo of a long colonnade with sunlight falling through the arches in sharp diagonal bands across the paved floor, with two people walking far off in the distance.
this exactly my point we can see that the light stay in sharp shape but we can observe it from other angles how the lights get to other angles
 
danielhaish said:
this exactly my point we can see that the light stay in sharp shape but we can observe it from other angles how the lights get to other angles
The light gets to other angles by reflection.
 
danielhaish said:
so my question is whether the light spreading or not
Sometimes it does, and sometimes the rays are almost parallel.
 
  • Like
Likes   Reactions: sophiecentaur and Dale
Not many natural light sources are points so the light does not all come from exactly the same direction. So the shadow will get more and more blurred as you get closer. Look up Umbra and Penumbra to see things like shadow softening and what you can really see during an eclipse.
Edit: BEG your pardon - the fuzz gets worse as you get further away. If the Moon went way beyond its present distance, (from us) our umbra would be so small that we would never get a total lunar eclipse. The Sun is so much bigger than us.
 
Last edited:
  • Like
Likes   Reactions: danielhaish and Dale