Advertisements
Advertisements
Question
The focal lengths of four convex lenses P, Q, R and S are 20 cm, 15 cm, 5 cm and 10 cm, respectively. The lens having greatest power is :
(a) P
(b) Q
(c) R
(d) S
Solution
R
Power=`1/"focal length"`
Therefore, a lens with a small focal length will have more power.
APPEARS IN
RELATED QUESTIONS
An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size and the nature of the image formed.
A beam of light travelling in air is incident of water. Draw a ray-diagram indicating the change in its path in water.
Define principal axis, principal focus and focal length of a convex lens.
List some things that convex lens and concave mirror have in common.
Name one simple optical instrument in which the above arrangement of convex lens is used.
An object 50 cm tall is placed on the principal axis of a convex lens. Its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens.
To find the image distance for varying object distances in case of a convex lens of focal length 15 cm, a student obtains on a screen a sharp image of a bright object by placing it at 20 cm distance from the lens. After that he gradually moves the object away from the lens and each time focuses the image on the screen.
(a) In which direction-towards or away from the lens does he move the screen to focus the object?
(b) How does the size of image change?
(c) Approximately at what distance does he obtain the image of magnification –1?
(d) How does the intensity of image change as the object moves farther and farther away from the lens?
For finding the focal length of a convex lens by obtaining the image of a distant object, one should use as the object.
(1) a well lit distant tree
(2) window grill in the class room
(3) any distant tree
(4) a lighted candle kept at the other end of the table.
A candle is placed between f and 2f a convex lens. Draw a ray diagram showing the position of the image.
Distinguish between:
Concave lens and Convex lens
