Producing umbra and penumbra with light sources

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Homework Help Overview

The discussion revolves around the concepts of umbra and penumbra in the context of light sources and shadow formation. Participants are exploring how many light sources need to be blocked to create different types of shadows when using multiple light sources.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are attempting to clarify the definitions of umbra and penumbra, as well as the conditions required to create these shadows with varying numbers of light sources. Questions about the definitions and the mechanics of shadow formation are raised, along with requests for help in understanding the concepts.

Discussion Status

The discussion is active, with participants sharing definitions and attempting to clarify their understanding of the terms. Some guidance has been offered regarding the relationships between light sources and shadow types, but there is no explicit consensus on the answers to the original questions posed.

Contextual Notes

Participants express uncertainty about the definitions of "dark penumbra" and "light penumbra," and there are indications of varying levels of understanding regarding the mechanics of shadow formation with multiple light sources.

queen2020
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when two souces are used, how many sources must be blocked by the object to produce the unbra? and the penumbra?

I looked it up in my textbook and on the internet and i still can't find the answer.
 
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help please

Can someone help me please
 
Both have to be blocked for the "umbra", only one for the "penumbra".
 
Do you know the definitions of umbra and penumbra? The answers should have been obvious. Even doing something as crude as punching

"define umbra"
"define penumbra"

into google and looking at the web definitions gives us phrases like:

For penumbra:
"Literally partial shadow; the partially lighted area around any completely darkened area (umbra) of full shadow."
"The shadow that results when only part of the bright object is occulted"
"region of partial shadow that is outside the umbra; the light source is partially blocked."

For umbra:
"The area of total darkness in the shadow caused by an eclipse."
"The umbra is the area of total shadow (compare to penumbra)."
"The portion of a shadow that receives no direct light from the light source."
 
thank you so much
 
I need help with shadows

When three sources are used, how many sources must be blocked by the object to produce the umbra? the dark penumbra? and the light penumbra?

Could anybody help me please.
 
Have you tried at all to figure it out yourself?
 
yes i have tried to figure it out but i can't figure it out at all
 
In your own words, what are the definitions of "umbra", "dark penumbra", and "light penumbra"?

Can you at least identify the conditions on being in the umbra or penumbra?
 
Last edited:
  • #10
The umbra is part of the shadow that is entirely dark. i don't know the definitions of dark penumbra or light penumbra.
 
  • #11
Ok, that's good. Can you describe the penumbra? Do you have a guess as to what "light penumbra" and "dark penumbra" mean? I think that "light" and "dark" weren't being used as technical terms here, just descriptive.
 
  • #12
so i would put a part where some light falls.
 
  • #13
I don't understand what you've suggested.
 
  • #14
When three sources are used, how many sources must be blocked by the object to produce the umbra? the dark penumbra? and the light penumbra?
 
  • #15
Didn't you already figure one of those questions out?
 
  • #16
i don't know
 
  • #17
queen2020 said:
i don't know

Draw yourself some diagrams. If you have one light source blocked by an object, there will be a shadow that has an umbra and a penumbra. If the shadow falls on a screen, you can draw the umbra and penumbra areas that hit the screen. I will assume you know what those are. If you have two light sources, each source will have its own umbra region and penumbra region behind the object. On a screen, there may or may not be some umbra overlap, some region where the umbra of one shadow overlays the penumbra of a second shadow, and some regions where only penumbra overlap. There could be no overlap at all if the screen is too far away from the object, but you can move the screen closer to get all the different kinds of overlap that are possible. With three sources you can have more combinations of overlap contitions including: three umbra overlap, two umbra and one penumbra, one umbra and two penumbra, three penumbra. Try to sketch these various possibilities as they might appear on a screen and then answer the question.
 

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