Question

1.
Rays from the sun converge at a point 15 cm in front of a concave mirror. Where the object should be placed so that the size of the image is equal to the size of the object? (a) 15 cm in front of the mirror
(b) 30 cm in front of the mirror
(c) Between 15 cm and 30 cm in front of the mirror.
(d) More than 30 cm in front of the mirror
1
2.
The laws of reflection holds good for
(a)Plane mirror
(b)Concave mirror only
(c)Convex mirror only
(d)All mirrors irrespective of the shape
1
3.
Read the given text and answer the following questions:
Rajesh is a student of class X and Ram is studying in class VII. Rajesh told Ram that he would show a magic to him. Rajesh had a lens. He focused the rays of sunlight on the bare arm of Ram. After few seconds, Ram felt pain and removed his arm away. Rajesh was laughing at Ram.
1. Name the type of lens used by Rajesh.
(a) Concave lens
(b) Convex lens
(c) Plano-concave lens
(d) Can be both concave and convex lens
2. Where the object is placed in front of lens in the given case:
(a) At focus
(b) At infinity
(c) Between pole and focus
(d) Beyond C
3. If Ram’s arm is at a distance of 17 cm from the lens , what is its centre of curvature (a) 17 cm
(b) 34 cm
(c) 8.5 cm
(d) None of these
4. What can be said about the size of the image?
(a) Very large
(b) Highly diminished
(c) Equal to the object
(d) None of these
5. What can you say about the nature of image formed in this case?
(a) Virtual and erect image
(b) Real and inverted image
(c) Virtual and inverted image
(d) Real and erect image

Answer 1

Answer:

It is given that sun rays converge at 15 cm. So, focal length of the mirror = f = 15 cm. In case of a concave mirror, the size of image and object will be same if the object is placed at 2f. Hence, in this case object must be place at 2f or 2 × 15 = 3

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