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Maharashtra State BoardSSC (English Medium) 10th Standard

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. - Science and Technology 1

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Question

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.

Diagram
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Solution

When an object is placed at the centre of curvature 2F1 of a convex lens, we will get a real image of the same size as the object.

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Chapter 7: Lenses - Exercises [Page 92]

RELATED QUESTIONS

A converging lens has focal length of 12 cm. Calculate at what distance the object should be placed from the lens so that it forms an image at 48 cm on the other side of the lens.


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 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.


An object of height 4 cm is placed at a distance of 20 cm from a concave lens of focal length 10 cm. Use lens formula to determine the position of the image formed.


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.


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 spherical mirror produces an image of magnification -1 on a screen placed at a distance of 50 cm from the mirror.

(a) Write the type of mirror.

(b) Find the distance of the image from the object.

(c) What is the focal length of the mirror?

(d) Draw the ray diagram to show the image formation in this case.


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


The image seen in a plane mirror cannot be formed on a screen. What name is given to this type of image?


When an object is placed at a distance of 50 cm from a concave spherical mirror, the magnification produced is, `-1/2`. Where should the object be placed to get a magnification of, `-1/5`? 


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.


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


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


If a magnification of, −1 (minus one) is to be obtained by using a converging mirror, then the object has to be placed:

(a) between pole and focus
(b) at the centre of curvature
(c) beyond the centre of curvature
(d) at infinity


In order to obtain a magnification of, −0.6 (minus 0.6) with a concave mirror, the object must be placed:

(a) at the focus
(b) between pole and focus
(c) between focus and centre of curvature
(d) beyond the centre of curvature


Explain what is meant by a virtual, magnified image. 


The lens A produces a magnification of, − 0.6 whereas lens B produces a magnification of + 0.6. 

What is the nature of lens B


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. 


The image of a candle flame placed at a distance 30 cm from a spherical lens is formed on a screen placed at a distance of 60 cm from the lens. Identify the type of lens and calculate its focal length. If the height of the flame is 2.4 cm, find the height of its image.


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


The image of a candle flame placed at a distance 36 cm from a spherical lens is formed on a screen placed at a distance of 72 cm from the lens. Identify the type of lens and calculate its focal length. If the height of the flame is 2.5 cm, find the height of its image.


Give a scientific reason.

Simple microscope is used for watch repairs.


Solve the following example.

An object kept 60 cm from a lens gives a virtual image 20 cm in front of the lens. What is the focal length of the lens? Is it a converging lens or diverging lens?


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.


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.


Find the position and magnification of the image of an object placed at distance of 8.0 cm in front of a convex lens of focal length 10.0 cm. Is the image erect or inverted?


The lens of the eye is flattened when looking at nearby objects.


The image of a candle flame formed by a lens is obtained on a screen placed on the other side of the lens. If the image is three times the size of the flame and the distance between lens and image is 80 cm, at what distance should the candle be placed from the lens? What is the nature of the image at a distance of 80 cm and the lens?


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?


The magnification by a lens is -3. Name the lens and state how are u and v related?


What information about the nature of image is erect or inverted, do you get from the sign of magnification + or -?


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