Question

1. The magnification produced by concave lens is always less than 1. Why? [1]

2. Which mirror has large vision area? [1]

3. Where on the principal axis of a concave mirror should an object be placed so that

the magnification produced by the mirror is -1? [1]

4. If virtual, errect and magnified image of an object is formed by convex lens; the

object must be at a distance ______. [1]

5. _____ is an instrument used to measure the power of a lens. [1]

6. When a ray of light travels from water to air, its speed _____. [1]

7. From which of the following letters (W, X, Y, Z) , can we obtain its laterally inverted

image? [1]

8. Write Snell’s law in mathematical form. [1]

9. An object is kept at 40 cm from a concave lens of focal length 60 cm. Find the

image distance. [1]

10. Find the focal length of a lens of ower -2.0 D. What type of lens is this? [1]

11. The optician’s prescription for a pair of spectacles is : [2]

Right eye: -3.5 D, Left eye: - 4.00 D.

(a) Are these lenses thinner at the middle or at the edges? (b) Which is the weaker eye?

12. Give reason: It is difficult to pierce a fish swimming in a river. [2]

13. With neat and labelled ray diagram describe the position, nature and relative size of

the image formed when an extended object AB is placed between principal focus F1

and optical centre O of a convex lens. [2]

14. A 2.0 cm tall object is placed perpendicular to the principal axis of a convex lens of

focal length 10 cm. The distance of the object from the lens is 15 cm. Find the nature,

position and size of the image. Also find the magnification. [3]

15. Write the uses of concave mirror. [3]

16. Explain the New Catresian sign convention (system) for reflection by a spherical

mirror. ​

Answer 1

Answer:

1. Concave lenses always produce images that are upright, virtual, reduced in size, and located on the object's side of the lens. Therefore, the magnification produced by a concave lens is always less than 1.
2. Because the image is smaller, more image can fit onto the mirror, so a convex mirror provides for a larger field of view than a plane mirror. This is why they are useful. They are used whenever a mirror with a large field of view is needed. For example, the passenger-side rear view mirror on a car is convex.
3. With a concave mirror, an object is placed at a distance x1 from the principal focus, on the principal axis. The image is formed at a distance x2 from the principal focus.