the soviet union was the first country.
The correct option is D.
Lumen is used to quantify the amount of total light energy that a source is putting out in all direction, thus, it refers to luminous output of a light source. Initial lumen refers to the luminosity of a light when it was first turned on; the luminosity is highest at this point.
Answer:
the umbra and penumbra
Explanation:
The two parts of a shadow are the umbra and penumbra.
A shadow is an expression formed when light from a source is cut blocked by an opaque body.
Most shadows are made up of two parts, umbra and penumbra.
- The umbra is the darkest, and the innermost part of a shadow.
- In the penumbra, only a portion of the light source is blocked. It is more of like a partial shadow.
The umbra is directly formed by light which impinges on an opaque body and it completely cut off.
They help scientists explain concepts that are difficult to observe.
