Figure 5.49 shows an object AB placed on the principal axis of a lens L. The two foci of the lens are $F_{1}$ and $F_{2}$ . The image formed by the lens is erect, virtual and diminished. Copy the diagram.

(a) What type of lens is it?
(b) Draw the outline of the lens (L) used.
(c) Draw a ray of light starting from B and passing through O. Show the same ray after refraction through the lens.
(d) Draw another ray from B, which after passing parallel to the principal axis, is incident on the lens and emerges after refraction from it. (d) Locate the final image formed.
[5 MARKS]

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Solution

part a: 2 Marks
part b,c and d: 1 Mark each

(a) When an object is placed beyond the focus, in a convex lens a real image is formed, while in a convex lens a virtual image is formed. In the above case, an erect image is formed so it is a concave lens.
The complete ray diagram is shown below in which A' B' is the final image formed by the lens.

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Similar questions

Q. The given figure shows an object AB, placed on the principal axis of a convex lens.

F_{1}

and

F_{2}

are the foci of lens Copy the diagram.

(a) Draw a ray of light from point B and passing through O. Show the same ray after refraction through the lens.
(b) Draw another ray from B, which passes through

F_{2}

, after refraction by the lens.
(c) Locate the final image formed.
(d) Is the image real or virtual?
(e) The image formed is inverted or erect?
[5 MARKS]

A ray of light after refraction through a convex lens emerges parallel to the principal axis. (a) Draw a ray diagram to show it. (b) The incident ray passes through a point F on the principal axis. Name the point F.

State whether the following statements are 'true' or 'false' by writing T/F against them.

(a) A convex lens has a divergent action and a concave lens has a convergent action.

(b) A concave lens, if kept at a proper distance from an object, can form its real image.

(d) A ray of light incident at the optical centre of lens, passes undeviated after refraction.

(e) A concave lens forms a magnified or diminished image depending on the distance of object from it.

Q. A ray of light is incident on a lens parallel to its principal axis. After refraction, the ray passes through or appear to come from :

Q. A ray of light from the object, parallel to the principal axis, after refraction from a convex lens, passes through ___.

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