1. A concave lens has focal length of 20 cm. At what distance from the lens a 5 cm tall object be placed so that it forms an image at 15 cm from the lens? Also calculate the size of the image formed. [Delhi]
   Answer.
   

2. An object 50 cm tall is placed on the principal axis of a convex lens. Its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens. [All India]
Answer.

3. Draw the ray diagram in each case to show the position and nature of the image formed when the object is placed:
(i) at the centre of curvature of a concave mirror
(ii) between the pole P and focus F of a concave mirror
(iii) in front of a convex mirror
(iv) at 2F of a convex lens
(v) in front of a concave lens
Answer.

Nature of image: Real, inverted and same size image is formed at the centre of curvature.

Nature of image: Virtual, enlarged and erect image is formed behind the mirror.

Nature of image: Virtual, erect and diminished, image is formed behind the mirror.

Nature of image: Real, inverted and size to size, image is formed at 2F on the other side of lens.

Nature of image: Virtual, erect and diminished image is formed between O and F on the same side of object.

4. If a light ray IM is incident on the surface AB as shown, identify the correct emergent ray. [Delhi (C)]

Answer. Ray NQ, as it has to be parallel to ray OS.

5. The refractive indices of four media A, B, C and D are given in the following table:

If light, travels from one medium to another, in which case the change in speed will be (i) minimum, (ii) maximum? [Delhi(C)]
Answer. (i) Minimum change is seen as light moves between 1.50 and 1.52, i.e. B and C.
(ii) Maximum change when light moves between 1.33 and 2.40, i.e. A and D.

6. “The refractive index of diamond is 2.42”. What is the meaning of this statement in relation to speed of light? [Delhi]
Answer.

7. Redraw the given diagram and show the path of the refracted ray: [All India(C)]

Answer.

8. Redraw the given diagram and show the path of the refracted ray: [All India(C)]

Answer.

9. Draw ray diagrams to represent the nature, position and relative size of the image formed by a convex lens for the object placed:
(a) at 2F₁
(b) between F₁ and the optical centre O of lens: [All India]
Answer.

10 .An object 2 cm in size is placed 30 cm in front of a concave mirror of focal length 15 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image? What will be the nature and the size of the image formed? Draw a ray diagram to show the formation of the image in this case. [Delhi(C)]
Answer.

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