Question

test your learning outcome

1. what is a lens? name two types of lenses.
2. describe the characteristics of (a) a convex lens, and a (b) concave lens.
3. why do we call a convex lens a convergent lens and concave lens a divergent lens.
4. how do we make fire with a convex lens?

Explanation:

1. A lens is a transparent refracting medium bounded by two - spherical surfaces or one spherical and one plane surface. Two types are convex and concave lenses.
2. (a) A convex lens is thicker at the middle and thinner at the edges. It converges light rays. (b) A concave lens is thinner at the middle and thicker at the edges. It diverges light rays.
3. A convex lens converges parallel rays of light to a point (principal focus), so it is called a convergent lens. A concave lens diverges parallel rays of light, so it is called a divergent lens.
4. We can make fire with a convex lens by using it to focus the sun's rays onto a small, combustible object. The convex lens converges the sun's rays to a point, increasing the intensity of the light and heat at that point until the object catches fire.

Answer:

1. A lens is a transparent refracting medium bounded by two - spherical surfaces or one spherical and one plane surface. Two types: convex and concave lenses.
2. (a) Convex lens: Thicker at middle, thinner at edges, converges light rays. (b) Concave lens: Thinner at middle, thicker at edges, diverges light rays.
3. Convex lens converges light, so convergent; concave lens diverges light, so divergent.
4. Use convex lens to focus sun's rays on a combustible object.