Advertisements
Advertisements
प्रश्न
A 4 cm tall object is placed on the principal axis of a convex lens. The distance of the object from the optical centre of the lens is 12 cm and its sharp image is formed at a distance of 24 cm from it on a screen on the other side of the lens. If the object is now moved a little away from the lens, in which way (towards the lens or away from the lens) will he have to move the screen to get a sharp image of the object on it again? How will the magnification of the image be affected?
Advertisements
उत्तर
Given that
Object distance, u = −12 cm
Image distance, v = 24 cm
`1/"f"=1/"v"-1/"u"`
`1/"f"=1/24-1/((-12))`
`1/"f"=1/8`
`therefore"f"=8cm`
The focal length of the lens is 8 cm.
Now if the object is moved away from the lens, the screen has to be moved towards the lens. This is because when we move the object away from the lens, the object distance is increased. Hence, by the lens formula, the image distance decreases.
Magnification is given as
`"m"="v"/"u"`
Because the image distance (v) decreases, the value of magnification also decreases.
APPEARS IN
संबंधित प्रश्न
Define the following term in the context of spherical mirrors:- Principal axis
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. |
A ray of light strikes a plane mirror at an angle of 40° to the mirror surface. What will be the angle of reflection?
The shiny outer surface of a hollow sphere of aluminium of radius 50 cm is to be used as a mirror:
What will be the focal length of this mirror?
A concave mirror can be used to produce a parallel beam of light. Draw a ray to illustrate this.
If the focal length of a spherical mirror is 10 cm, what is the value of its radius of curvature?
A shopkeeper wanted to fix a mirror which will give a maximum view of his shop. What type of mirror should he use? Give reason.
