Advertisements
Advertisements
प्रश्न
Solve the following example.
5 cm high object is placed at a distance of 25 cm from a converging lens of focal length of 10 cm. Determine the position, size and type of the image.
Advertisements
उत्तर
Given:
Height of object, ho = 5 cm
Object distance, u = -25 cm
Since the lens is converging, thus it is a convex lens.
Focal length of the lens, f = 10 cm
Using lens formula,
\[\frac{1}{v} - \frac{1}{u} = \frac{1}{f}\]
\[ \Rightarrow \frac{1}{v} = \frac{1}{10} + \frac{1}{- 25} = \frac{3}{50}\]
\[ \Rightarrow v = \frac{50}{3} = 16 . 7 cm\]
Thus, the image is formed
16 . 7 cm right of the lens.
Now, we know
\[\frac{v}{u} = \frac{h_i}{h_o}\]
\[ \Rightarrow h_i = \frac{50}{3 \times - 25} \times 5 = -\frac{10}{3} = - 3 . 3 \text{cm}\]
Thus, the size of the image is 3.3 cm. Negative sign shows that the image formed is real and inverted. Hence, the image formed is real and inverted and diminished.
APPEARS IN
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.
The image formed by a spherical mirror is real, inverted and is of magnification −2. If the image is at a distance of 30 cm from the mirror, where is the object placed? Find the focal length of the mirror. List two characteristics of the image formed if the object is moved 10 cm towards the mirror.
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.
A student wants to project the image of a candle flame on a screen 60 cm in front of a mirror by keeping the flame at a distance of 15 cm from its pole.
(a) Write the type of mirror he should use.
(b) Find the linear magnification of the image produced.
(c) What is the distance between the object and its image?
(d) Draw a ray diagram to show the image formation in this case.
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
An object is held 20 cm away from a converging lens of focal length 10 cm. Find the position of the image formed.
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
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
Linear magnification (m) produced by a rear view mirror fitted in vehicles:
(a) is equal to one
(b) is less than one
(c) is more than one
(d) can be more less than one depending on the position of object
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?
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.
The lens A produces a magnification of, − 0.6 whereas lens B produces a magnification of + 0.6.
What is the nature of lens A?
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?
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.
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.
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.
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.
An object is placed at a distance of 20 cm in front of a concave lens of focal length 20 cm.
- Find the position of the image, and
- the magnification of the image.
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.
Magnification of a convex lens is ______.
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 magnification produced when an object is placed at a distance of 20 cm from a spherical mirror is +1/2. Where should the object be placed to reduce the magnification to +1/3.
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.
What information about the nature of image is erect or inverted, do you get from the sign of magnification + or -?
