A lens that is thinner at the middle and thicher at the edges is

Analyze the question: The question asks what kind of lens is thinner at the middle and thicker at the edges.

Concept:

• A converging (convex) lens is thicker at the middle and thinner at the edges. It brings parallel rays of light together at a focus.
• A diverging (concave) lens is thinner at the middle and thicker at the edges. It spreads parallel rays apart, so they appear to come from a virtual focus.

Solution:

1. The lens described is thinner at the centre and thicker at the rim.
2. That shape is a concave lens, which is a diverging lens.
3. Check the other options: • B. Converging: this is thicker in the middle, so it is wrong. • C. Plano-convex: one face is flat and the other bulges outward, so it is thicker in the middle. It is a type of converging lens, so it is wrong. • D. Converging meniscus: it is thicker at the centre, so it is wrong.

Answer: A. Diverging

Exam tip: Remember "Concave = Caves in at the middle = Diverging." A convex lens bulges out like a belly, so it is thick in the middle and converging. Also remember that any lens with a thick centre converges, and any lens with a thin centre diverges.