Question

A lens is a piece of any transparent material bounded by two curved surfaces. There are two types of lenses convex lens and concave lens.

Convex lens is made up of a transparent medium bounded by two spherical surfaces such that thicker at the middle and thinner at the edges. Concave lens is also made up of a transparent medium such that thicker at the edge and thinner at the middle. The mid point of the lens is called optical centre.
A point on the principal axis, where the incident parallel rays meet or appears to come out after refraction is called focus.
A convex lens converges a parallel beam of light to other side whereas concave lens spreads out.
(i) Which of the following lenses would you prefer to use while reading small letters found in dictionary?
(a) A convex lens of focal length 50 cm
(b) A concave lens of focal length 50 cm
(c) A convex lens of focal length 5 cm
(d) A concave lens of focal length 5 cm
(ii) Which type oflenes are shown in given figure (i) and (ii).

(a) Plano concave, concavo convex
(b) Plano convex, convexo concave
(c) Double concave, concave convex
(d) Convexo concave, double convex
(iii) A small bulb is placed at the focal point of a converging lens. When the bulb is switched on, the lens produces
(a) a convergent beam of light
(b) a divergent beam of light
(c) a parallel beam of light
(d) a patch of coloured light
(iv) The part oflens through which the refraction takes place is called
(a) aperture (b) centre of curvature
(c) principal axis (d) focus
(v) A water drop acts as a
(a) convex lens (b) concave lens
(c) double concave lens (d) none of these
plz answer it

Answer 1

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Answer 2

Answers are given below:

Explanation:

1. Option (d) . A convex lens of focal length 5 cm will be preferred here. A convex lens gives a magnified image . Also shorter focal length gives better magnification.
2. Image is not provided
3. Option (c) , parallel beam of light will be produced. When a bulb is placed near the convex lens which acts as a converging lens then it tends to refract the rays . The emergent refracted rays will now be parallel to each other.
4. Option (a) , aperture is the correct answer. The part of lens through which refraction occurs is called the aperture. It is the diameter of the circular outline of the spherical lens.