Advertisements
Advertisements
Question
An illuminated object lies at a distance 1.0 m from a screen. A convex lens is used to form the image of the object on a screen placed at a distance of 75 cm from the lens. Find:
- the focal length of the lens, and
- the magnification.
Advertisements
Solution
Distance of object from screen = 1.0 m = 100 cm
v = 75 cm,
u = 100 – 75 = 25 cm = -25 cm
(i) f = ?
`1/"f" = 1/"v" -1/"u"`
= `1/75 - (1/-25)`
= `1/75 + 1/25`
`1/"f" = (1 + 3)/75 = 4/75`
f = `75/4`
f = 18.75
(ii) Magnification (m) = `v/u = 75/-25 = -3`
Magnification (m) = 3
The -ve symbol indicates that the created image is actual and inverted.
APPEARS IN
RELATED QUESTIONS
The following diagram shows an object AB and a converging lens L with foci F1 and F2 State three characteristics of the image in relation to the object.
A lens forms an erect, magnified, and virtual image of an object. Name the device which uses this principle.
If the magnification produced by a lens is - 0.5, the correct statement is ______.
The focal length of a convex lens is 25 cm. At what distance from the optical centre of the lens an object be placed to obtain a virtual image of twice the size?
The maximum magnifying power of a convex lens of focal length 5 cm can be ______.
Name the lens used as a magnifying glass.
A convex lens produces on a screen an image twice the size of the object. If the position of image and object be interchanged, what will be the magnification then?
What is a simple microscope or a magnifying glass? Draw a ray diagram to show its function.
Copy and complete the following ray diagram.
(i) Draw a ray diagram to show how the lens can be used as a ‘magnifying glass’? State the nature of the lens.
(ii) In what respect does the image in (i) above different from the image formed by a concave lens?
