Light rays travel from a source in a straight line. If an opaque (solid) object gets in the way, it stops light rays from traveling through it. An opaque object is an object through which no light can pass. One such example is your body. Since light cannot pass through your body, it forms a dark region behind. This dark region where the light cannot reach is known as a shadow. Light travels in straight lights and so cannot bend around your body, which is why you see a shadow. The size and shape of a shadow depend on the position and size of the light source with respect to the object.

Opaque objects form clear dark shadows. A transparent object does not make any shadow as light passes straight through it. Translucent objects create faint shadows as light is able to pass partially through them.

Key terms

• The dark region behind an opaque object where light cannot reach is known as a shadow.