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 focus
An image that cannot be obtained on a screen is called ______.
A ray of light strikes a plane mirror at an angle of 40° to the mirror surface. What will be the angle of reflection?
A student obtained a sharp image of a burning candle, placed at the farther end of a laboratory table, on a screen using a concave mirror. For getting better value of focal length of the mirror, the subject teacher suggested him for focusing a well illuminated distant object. What should the student do?
(A) He should move the mirror away from the screen.
(B) He should move the mirror slightly towards the screen.
(C) He should move the mirror as well as the screen towards the newly selected object.
(D) He should move only the screen towards the newly selected object.
A straight stick partly dipped in water obliquely appears to be bent at the surface of the water.
Draw a ray diagram to show the formation of the image, when the object is placed between optical centre and principal focus of a convex lens.
State the signs and values of magnifications in the above mentioned case.
The diagram below shows the parallel rays incident on a convex mirror. C is the centre of the curvature of the mirror. By drawing the paths of the reflected rays, label the focus F and hence find the focal length of the mirror.
