Q1.
When the opaque object was a shiny object like a polished steel plate, I got a shadow on the screen, but I also saw that there was a bright spot of light on the wall on the opposite side. Why was it so?
Answer
Because a polished steel plate does two things at the same time. It is opaque, so it stops the light and makes a shadow behind it. It is also shiny, so it does not absorb that light — it throws it back in a new direction, and the returning light makes a bright spot on the opposite wall.
Light from torch → steel plate → reflected → bright spot on the opposite wall
Behind the plate → no light → shadow
Behind the plate → no light → shadow
Why it happens: A rough, dull surface such as cardboard scatters the light it receives in all directions, so no bright patch is formed anywhere. A smooth, polished surface sends almost all the light away together in one direction. This change of direction of light by a shiny surface is called the reflection of light.