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प्रश्न
Give a scientific reason.
Simple microscope is used for watch repairs.
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उत्तर १
- When an object is put inside the focal length of a magnifying glass or simple microscope (convex lens), the larger and erect image appears on the same side of the lens as the object.
- By altering the distance between the object and the lens, the image can be obtained at the shortest distance of distinct vision. Thus, a watch repairer may see the minute parts of a watch more clearly with the use of a magnifying glass (a rudimentary microscope) than with the naked eye, and without putting any strain on the eye. As a result, watch repairers utilise a magnifying glass (a basic microscope) to repair the timepieces.
उत्तर २
- In a simple microscope, a convex lens with a small focal length is used.
- It produces a virtual, erect, and bigger image of an object.
- We can get a 20 times larger image of an object using a simple microscope.
Hence, watch repairers use a simple microscope while repairing watches.
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संबंधित प्रश्न
A divergent lens of focal length 30 cm forms the image of an object of size 6 cm on the same side as the object at a distance of 15 cm from its optical centre. Use lens formula to determine the distance of the object from the lens and the size of the image formed.
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
At what distance from a concave lens of focal length 20 cm, should a 6 cm tall object be placed so that it forms an image at 15 cm from the lens ? Also determine the size of the image formed.
A student has obtained an image of a distant object on a screen to determine the focal length F1 of the given lens. His teacher, after checking the image, gave him another lens of focal length F2 and asked him to focus the same object on the same screen. The student found that to obtain a sharp image, he has to move the lens away from the screen. From this finding, we may conclude that both the lenses given to the student were :
(A) Concave and F1 < F2
(B) Convex and F1 < F2
(C) Convex and F1 > F2
(D) Concave and F1 > F2
A student was asked by his teacher to find the image distance for various object distance in case of a given convex lens. He performed the experiment with all precautions and noted down his observations in the following table:
| S. No. |
Object distance (cm) |
Image distance (cm) |
| 1 | 60 | 15 |
| 2 | 48 | 16 |
| 3 | 36 | 21 |
| 4 | 24 | 24 |
| 5 | 18 | 36 |
| 6 | 16 | 48 |
After checking the observations table the teacher pointed out that there is a mistake in recording the image distance in one of the observations. Find the serial number of the observations having faulty image distance.
(A) 2
(B) 3
(C) 5
(D) 6
An object is held 20 cm away from a converging lens of focal length 10 cm. Find the position of the image formed.
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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
In order to obtain a magnification of −2 (minus 2) with a concave mirror, the object should be placed:
(a) between pole and focus
(b) between focus and centre of curvature
(c) at the centre of curvature
(d) beyond the centre of curvature
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(a) at the focus
(b) between pole and focus
(c) between focus and centre of curvature
(d) beyond the centre of curvature
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Explain what is meant by a virtual, magnified image.
Draw a ray diagram to show the formation of a virtual magnified image of an object by a convex lens. In your diagram, the position of object and image with respect to the principal focus should be shown clearly.
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.
To determine focal length of a concave mirror a student obtains the image of a well lit distant object on a screen. To determine the focal length of the given concave mirror he needs to measure the distance between:
(A) mirror and the object
(B) mirror and the screen
(C) screen and the object
(D) screen and the object and also mirror and the screen
At what distance should an object be placed from a lens of focal length 25 cm to obtain its image on a screen placed on the other side at a distance of 50 cm from the lens? What will be the magnification produced in this case?
At which position will you keep an object in front of a convex lens so as to get a real image of the same size as the object? Draw a figure.
A lens forms the image of an object placed at a distance 15 cm from it, at a distance 60 cm in front of it. Find the magnification.
Magnification of a convex lens is ______.
A lens of focal length 5 cm is being used by Debashree in the laboratory as a magnifying glass. Her least distance of distinct vision is 25 cm.
- What is the magnification obtained by using the glass?
- She keeps a book at a distance 10 cm from her eyes and tries to read. She is unable to read. What is the reason for this?
Ravi kept a book at a distance of 10 cm from the eyes of his friend Hari. Hari is not able to read anything written in the book. Give reasons for this?
The focal length of a concave lens is 20 cm. At what distance from the lens should a 5 cm tall object be placed so that its image is formed at a distance of 15 cm from the lens? Also calculate the size of the image formed.
In a reading glass what is the position of the object with respect to the convex lens used?
Write an expression for magnification for a lens, explaining the meaning of the symbols used.
