Question

In a room lighted by an electric bulb, it is found that the shadow of the ceiling fan hanging in the center is falling on a wall opposite to the door. What can you say about the position of the bulb?
A) on the wall having the door
B) on the wall facing the door
C) on the wall on your right as you enter the room
D) on the wall on your left as you enter the room

Answer 1

Hint: A shadow is created when we put an object in the path of a light source. That means a shadow is just a region, where there is a lack of light because an opaque object is blocking light rays. The position of the shadow depends upon the position of light rays i.e. from where the rays are coming.

Complete step by step answer:
A shadow is created when we put an object in the path of a light source. That means a shadow is just a region, where there is a lack of light because an opaque object is blocking light rays. The position of the shadow depends upon the position of light rays i.e. from where the rays are coming.
Now if an electric bulb is lighting a room and the shadow of a ceiling fan that is hanging in the centre is shown on a wall opposite the door then we must say the fan is the object which is blocking the rays coming from the bulb.
Therefore, the bulb must be on the wall where the door is situated.
Now we consider the give options to find the correct analysis of the question:

(A) The position of the bulb is on the wall having the door – this should be the right option as we mention above that the bulb must be in the wall where the door is situated because the shadow of the fan is falling on the wall opposite the door and that's why the fan is the object which is blocking the rays coming from the bulb.

(B) The position of the bulb is on the wall facing the door – this can’t be true because the shadow is falling on the wall facing the door and that's why the source of the light and the shadow cannot be situated at the same side.

(C) The position of the bulb is on the wall on your right as you enter the room - this can’t be true because the shadow we see is on the wall facing the door, so if the bulb is on the right-sided wall the shadow must be in it’s the opposite wall.

(D) The position of the bulb is on the wall on your left as you enter the room - this can’t be true because the shadow we see is on the wall facing the door, so if the bulb is on the left-sided wall the shadow must be in it's opposite wall.

Hence, the right answer is an option (A).

Note:
If we decrease the distance between source and object, the blockage portion is increased and so the size of the shadow is more. And also, if we increase the distance between the object and the source the object cannot affect much on the light and that's why the shadow becomes small.