Question

question 1
which of these accurately describes an umbra?
a. an umbra only forms on flat surfaces.
b. an umbra is only visible during nighttime.
c. an umbra is the darker, center part of a shadow.
d. an umbra is the part of a shadow that allows some light from a given light source.
incorrect! please try again.

Explanation:

An umbra is the darkest part of a shadow where all light from the source is blocked. It doesn't depend on the surface being flat (so A is wrong). It can be visible during the day (like during a solar eclipse, so B is wrong). The part of the shadow that allows some light is the penumbra (so D is wrong).

Answer:

C. An umbra is the darker, center part of a shadow.