Advertisements
Advertisements
प्रश्न
A concave lens produces an image 20 cm from the lens of an object placed 30 cm from the lens. The focal length of the lens is:
(a) 50 cm
(b) 40 cm
(c) 60 cm
(d) 30 cm
उत्तर
60 cm
Object distance from the lens, u =-30 cm
Image distance from the lens, v =-20 cm
Using the lens formula, we get:
`1/f=1/v-1/u`
`1/f=1/-20-1/-30`
`1/f=1/-20+1/30`
`1/f=(-3+2)/60=1/60`
∴ f =- 60 cm
Therefore, the focal length of the lens is 60 cm.
APPEARS IN
संबंधित प्रश्न
Match the items given in Column I with one or more items of Column II.
| Column I | Column II | ||
| (a) | A plane mirror | (i) | Used as a magnifying glass. |
| (b) | A convex mirror | (ii) | Can form image of objects spread over a large area. |
| (c) | A convex lens | (iii) | Used by dentists to see enlarged image of teeth. |
| (d) | A concave mirror | (iv) | The image is always inverted and magnified. |
| (e) | A concave lens | (v) | The image is erect and of the same size as the object. |
| (vi) | The image is erect and smaller in size than the object. |
The shiny outer surface of a hollow sphere of aluminium of radius 50 cm is to be used as a mirror:
Which type of spherical mirror will it provide?
Draw a ray diagram to show the formation of image by a concave mirror for the object beyond its centre of curvature. State three characteristics of the image.
State whether the image in part (a) is real or virtual?
Why does a driver use a convex mirror instead of a plane mirror as a rear view mirror?
Illustrate your answer with the help of a ray diagram.
State the kind of mirror used
(a) By a dentist,
(b) As a search-light reflector.
Define the term Centre of curvature.
The spherical mirror used in a beauty parlour as make-up mirror is _______.
