Question

What is a lens? Describe the terms associated with a convex lens. List any two uses of lenses.​
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Answer 1

Answer:

A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction.

Convex lenses are thicker at the middle. Rays of light that pass through the lens are brought closer together (they converge). A convex lens is a converging lens.

When parallel rays of light pass through a convex lens the refracted rays converge at one point called the principal focus.

The distance between the principal focus and the centre of the lens is called the focal length.

Centre of curvature (C): The centre of sphere of which lens is a part.

Radius of curvature (R): The radius of sphere of which lens is a part.

Principal axis: Line joining the centre of curvatures of two lenses.

Optical centre (O): The point on the principal axis of a thin lens through which a ray of light passes undeviated.

First focal point (F1): It is a point on the principal axis of the lens such that the rays of light starting from it (convex lens) or appearing to meet at the point (concave lens) after refraction from the two surfaces of the lens become parallel to the principal axis of the lens.

Second focal point (F2): It is a point on the principal axis of the lens such that the rays of light parallel to the principal axis of the lens after refraction from both the surfaces of the lens pass through this point (convex lens) or appear to be coming from this point.

Focal plane: Plane passing through focus and perpendicular to the principal axis.

Uses of convex lens:

Magnifying glasses

Eyeglasses

Cameras

Microscopes