Identify the device used as a spherical mirror or lens in the following cases, when the image formed is virtual and erect in each case. (a) Object is placed between the device and its focus, an image formed is enlarged and behind it. (b) Object is placed between the focus and device, an image formed is enlarged and on the same side as that of the object. (c) Object is placed between infinity and device, an image formed is diminished and between focus and optical centre on the same side as that of the object. (d) Object is placed between infinity and device, image formed is diminished and between pole and focus, behind it.

Answer:

(a) Concave mirror

(b) Convex lens

(c) Concave lens

(d) Convex mirror

Convex lens

  • A convex lens is a lens with an outward curve. The thickness at the centre of a convex lens is more than the thickness at the edges of the lens.
  • Convex lenses are converging lenses. They have the ability to converge a parallel beam of light into a point.
  • The lens found in the human eye is a prime example of a convex lens.

Concave lens

  • A concave lens is a type of lens with at least one side curved inwards. A concave lens with both sides curved inward is known as a biconcave lens.
  • Concave lenses are diverging lenses, that is, they spread out light rays that have been refracted through them.
  • They have the ability to diverge a parallel beam of light.
  • For a concave lens, the edges are wider than the centre or the centre is thinner than the edges. Concave lenses are used in spectacles in order to overcome myopia or short-sightedness.

Concave mirror

In the case of a concave mirror, an image may be real or virtual, inverted or erect and magnified or diminished depending upon the position of the object.

Convex mirror

In the case of a convex mirror, an image formed will always be virtual, erect and diminished in spite of the position of the object.

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