(a) If the image formed by a lens is diminished in size and erect, for all positions of the object, what type of lens is it? (b) Name the point on the lens through which a ray of light passes undeviated. (c) An object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 30 cm. Find (i) the position (ii) the magnification and (iii) the nature of the image formed. - Zigya
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(a) If the image formed by a lens is diminished in size and erect, for all positions of the object, what type of lens is it?

(b) Name the point on the lens through which a ray of light passes undeviated.

(c) An object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 30 cm. Find (i) the position (ii) the magnification and (iii) the nature of the image formed.


(a) If the image formed by a lens is diminished in size and erect, for all positions of the object, then the lens is a concave lens.

(b) The point on the lens through which a ray of light passes undeviating is known as Pole.

(c) Given,

Object distance, u = -30 cm

Focal length, f =20 cm

i) Now, using the len’s formula,

 1 over straight f space equals 1 over straight v minus 1 over straight u

1 over straight v equals 1 over straight f plus 1 over straight u

straight v equals fraction numerator straight u space xf over denominator straight u plus straight f end fraction

straight v equals fraction numerator left parenthesis negative 30 right parenthesis straight x 20 over denominator 20 minus 30 end fraction
straight v equals space 60 space cm

The space image space is space formed space at space straight a space distance space of space 60 cm space of space the space other space side space of space the space optical space centre.
ii right parenthesis space Magnification comma space straight m equals straight m equals space minus straight v over straight u space equals negative fraction numerator 60 over denominator negative 30 end fraction space equals 2

 (iii) Image formed is inverted.

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