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प्रश्न
Draw a diagram to show how a converging lens held close to the eye acts as a magnifying glass. Why is it usual to choose a lens of short focal length for this purpose rather than one of long focal length?
उत्तर
Magnifying glass:
A lens with a short focal length is used so as to obtain greater magnification.
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संबंधित प्रश्न
A student is using a convex lens of focal length 10 cm to study the image formation by a convex lens for the various positions of the object. In one of his observations, he may observe that when the object is placed at a distance of 20 cm from the lens, its image is formed at (select the correct option)
(A) 20 cm on the other side of the lens and is of the same size, real and erect.
(B) 40 cm on the other side of the lens and is magnified, real and inverted.
(C) 20 cm on the other side of the lens and is of the same size, real and inverted.
(D) 20 cm on the other side of the lens and is of the same size, virtual and erect.
A student has obtained a point image of a distant object using the given convex lens. To find the focal length of the lens he should measure the distance between the :
(A) lens and the object only
(B) lens and the screen only
(C) object and the image only
(D) lens and the object and also between the object and the image
The image of a candle flame placed at a distance of 30 cm from a spherical lens is formed on a screen placed on the other side of the lens at a distance of 60 cm from the optical centre of the lens. Identify the type of lens and calculate its focal length. If the height of the flame is 3 cm, find the height of its image.
An object is placed (a) 20 cm, (b) 4 cm, in front of a concave mirror of focal length 12 cm. Find the nature and position of the image formed in each case.
Magnification produced by a convex mirror is always:
(a) more than 1
(b) less than 1
(c) equal to 1
(d) more or less than 1
A concave mirror produces magnification of +4. The object is placed:
(a) at the focus
(b) between focus and centre of curvature
(c) between focus and pole
(d) between the centre of curvature
A student wants to project the image of a candle flame on a screen 80 cm in front of a mirror by keeping the candle flame at a distance of 20 cm from its pole.
- Which type of mirror should the student use?
- Find the magnification of the image produced.
- Find the distance between the object and its image.
- Draw a ray diagram to show the image formation in this case and mark the distance between the object and its image.
An object of height 6 cm is placed perpendicular to the principal axis of a concave lens of focal length 5 cm. Use lens formula to determine the position, size and nature of the image if the distance of the object from the lens is 10 cm.
At which position will you keep an object in front of convex lens to get a real image smaller than the object? Draw a figure.
Write an expression for magnification for a lens, explaining the meaning of the symbols used.
