State the conditions when only the penumbra of an opaque object is obtained on the screen.

Conditions for obtaining penumbra of an opaque object are :

1. The light source must be extended (i.e., not a point source). Examples : tube light, the Sun, or a bulb.

2. Size of source of light must be bigger than the size of the opaque object.

3. The opaque object should be very close to the light source, and

4. The screen must be placed far away from the object and close to the edge of the shadow region.