A concave lens; doesn't have a focus because

It doesn't converge a parallel beam of light falling on it on a single point.

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Both it's surfaces are concave

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It has a focus; where all the diverging rays appear to meet.

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Solution

The correct option is C It has a focus; where all the diverging rays appear to meet.
Ofcourse a concave lens; diverges the parallel beam of rays falling on it. But it's not like the 'focus' is not defined for it. The focus of a concave lens is defined as the point where all the diverging rays appear to meet.

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Similar questions

Q. Parallel rays of light, falling on a concave lens, appear to diverge from a point

(a) at infinity
(b) at twice focal length
(c) at the focus
(d) between focus and the lens

A concave mirror can converge parallel beams of light at one point. But rays originating from the focus after reflection does not always travel parallel to the principal axis.

Q. A concave lens converges the parallel light rays incident on it.

A beam of light incident on a thin concave lens parallel to its principle axis diverges and appears to come from a point F on the principal axis. Name the point F. Draw a ray diagram to show it.

(a) With the help of a labelled diagram explain how a convex lens converges a beam of parallel light rays. Mark the principal axis, optical centre, principal focus and focal length of the convex lens on the diagram.
(b) State whether the convex lens has a real focus or a virtual focus. (c) List some things that convex lens and concave mirror have in common.

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