Question

when will multiple shadows be formed

Answer 1

when any opaque object experience light from many directions
and reflects those lights
then we are able to see many shadows
(multiple shadows)
for eg:- when you stand in between of stadium at the time of night then you will able to see as many as 4 shadows of yourself
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Answer 2

the absence of light. Shadow is form from an opaque or translucent object blocking a light source (since light travels in a straight line).

I'd explain this by setting up a diagram of the situation.  Each bulb can be thought to emit light rays in all directions.  Any place the light rays reach ends up being lit up by the bulb.  Now, draw a bunch of light rays heading from the bulb towards the pencil.  Any rays blocked by the pencil don't reach the other side, so that bulb casts a shadow there.  The size of the shadow depends on the distances you specified and the size of the pencil.  When you repeat this for all four bulbs, you can see how the shadows overlap and where they're separated.  In order to see four shadows, the four shadow regions need to be separated from each other.  I haven't done the math for your numbers, but if you see four distinct shadows, that must be the case.