Advertisements
Advertisements
प्रश्न
A student did an experiment with a convex lens. He put an object at different distances 25 cm, 30 cm, 40 cm, 60 cm and 120 cm from the lens. In each case he measured the distance of the image from the lens. His results were 100 cm, 24 cm, 60 cm, 30 cm and 40 cm, respectively. Unfortunately his results are written in wrong order.
What is the focal length of this lens?
उत्तर
The image of an object at 2f is formed at 2f. This means that the pair of u and v that is equal in value gives us the value of 2f, which is 40. Hence, the value of f (focal length) is `40/2.`
∴ f = 20 cm.
APPEARS IN
संबंधित प्रश्न
To find the image-distance for varying object-distances in case of a convex lens, a student obtains on a screen a sharp image of a bright object placed very far from the lens. After that he gradually moves the object towards the lens and each time focuses its image of the screen.
(a) In which direction – towards or away from the lens, does he move the screen to focus the object?
(b) What happens to the size of image – does it increase or decrease?
(c) What happen when he moves the object very close to the lens?
If you focus the image of a distant object, whose shape is given below, on a screen using a convex lens, the shape of the image of this object on the screen would be:
(a)
(b)
(c)
(d)
Where should an object be placed in front of a convex lens so as to obtain its real, inverted and magnified image?
In a certain murder investigation, it was important to discover whether the victim was long-sighted or short-sighted. How could a detective decide by examining his spectacles?
In the following cases, where must an object be placed in front of a convex lens so that the image formed is at infinity?
Yesh find out F1 and F2 of symmetric convex lens experimentally then which conclusion is true.
Answer the following question.
List four precautions which a student should observe while determining the focal length of a given convex lens by obtaining an image of a distant object on a screen.
State the position of object, position of image, nature of image when: Convex lens is used in observing biological specimens.
Define the terms principal foci and focal lengths as applied to a convex lens, and show them with the help of proper diagrams.
Find the odd one out and give its explanation.
