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 - Science

Advertisements
Advertisements

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

Advertisements

Solution

In the given case, the student has obtained the point image of a distant object using a convex lens.

According to the lens formula,

`1/f=1/v-1/u`

Here,

v = Image distance

u = Object distance

f = Focal length of the lens

Because the object is placed very far, the object distance is taken to be infinity. As u = ∞

`"Thus, "1/u=0" and "f="v"`

To find the focal length of the lens, the student should know the image distance, which is the distance between the lens and the screen.

Hence, the correct option is B.

  Is there an error in this question or solution?
2014-2015 (March) Delhi Set 1

Video TutorialsVIEW ALL [1]

RELATED QUESTIONS

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 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.


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


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?


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.

(i) Which type of mirror should the student use?

(ii) Find the magnification of the image produced.

(iii) Find the distance between the object and its image.

(iv) Draw a ray diagram to show the image formation in this case and mark the distance between the object and 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 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 scientific reason.

Simple microscope is used for watch repairs.


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.


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.


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


An object is placed vertically at a distance of 20 cm from a convex lens. If the height of the object is 5 cm and the focal length of the lens is 10 cm, what will be the position, size and nature of the image? How much bigger as compared to the object?


Magnification of a convex lens is


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?


Share
Notifications



      Forgot password?
Use app×