Advertisements
Advertisements
Question
The above image shows a thin lens with a focal length of 5m.
- What is the kind of lens shown in the above figure?
- If a real inverted image is to be formed by this lens at a distance of 7m from the optical centre, then show with calculation where should the object be placed.
- Draw a neatly labelled diagram of the image formation mentioned in (ii).
Solution
- Convex lens
- `1/f = 1/v - 1/u`
In this case, v = 7m and f = 5m
Putting the values in the equation, we get,
`1/5 = 1/7 - 1/u`
`1/u = 1/7 - 1/5 = (5 - 7)/35 = (-2)/35`
`u = -35/2 = -17.5` m
The object will be placed 17.5 m on the left of the convex lens. 
(two rays, arrows, and object placed beyond 2f on the left)
APPEARS IN
RELATED QUESTIONS
Analyse the following observation table showing variation of image-distance (v) with object-distance (u) in case of a convex lens and answer the questions that follow without doing any calculations :
| S. No. | Object-Distance u (cm) |
Image-Distance v (cm) |
| 1 | –100 | +25 |
| 2 | –60 | +30 |
| 3 | –40 | +40 |
| 4 | –30 | +60 |
| 5 | –25 | +100 |
| 6 | –15 | +120 |
(a) What is the focal length of the convex lens? Give reason to justify your answer.
(b) Write the serial number of the observation which is not correct. On what basis have you arrived at this conclusion?
(c) Select an appropriate scale and draw a ray diagram for the observation at S.No. 2. Also find the approximate value of magnification.
List some things that convex lens and concave mirror have in common.
An object 2 cm tall is placed on the axis of a convex lens of focal length 5 cm at a distance of 10 m from the optical centre of the lens. Find the nature, position and size of the image formed. Which case of image formation by convex lenses is illustrated by this example?
What kind of lens can form:
an erect magnified image?
Study the diagram below.
what are the points O, O’ called?
Point out the difference between a convex lens and a concave lens.
State the position of object, position of image, nature of image when: Convex lens is used as objective lens of photographic camera.
Diagram shows an object AB placed on the principal axis B of a convex lens placed in air. F1 and F2 are the two foci of the lens.
(i) Copy the diagram:
Draw a ray of light starting from B and passing through O. Show the same ray after refraction by the lens. Draw another ray from B which passes through F2 after refraction by the lens. Locate the final image
(ii) Is the image real or virtual?
Define the terms principal foci and focal lengths as applied to a convex lens, and show them with the help of proper diagrams.
Distinguish between:
Concave lens and Convex Lens
