State Two Applications Each of a Convex Lens and Concave Lens. - Physics

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Short Note

State two applications each of a convex lens and concave lens.

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Solution

The two applications of a convex lens are:-

(i) It is used as an objective lens in a telescope, camera, slide projector, etc.

(ii) With its short focal length it is also used as a magnifying glass.

The two applications of a concave lens are:-

(i) A person suffering from short sightedness or myopia wears spectacles having concave lens.

(ii)A concave lens is used as eye lens in a Galilean telescope to obtain an erect final image of the object.

Concept: Convex Lens
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Chapter 5: Refraction through a Lens - Exercise 5 (D) 1 [Page 131]

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Selina Concise Physics Class 10 ICSE
Chapter 5 Refraction through a Lens
Exercise 5 (D) 1 | Q 5 | Page 131

RELATED QUESTIONS

A student is using a convex lens of focal length 18 cm to study the image formation by it for the various positions of the object. He observes that when he places the object at 27 cm, the location of the image is at 54 cm on the other side of the lens. Identify from the following diagram the three rays that are obeying the laws of refraction and may be used to draw the corresponding ray diagram.

(A) 1, 2 and 4

(B) 1, 3 and 5

(C) 2, 4 and 5

(D) 2, 3 and 4


(a) Draw a ray diagram to show the formation of an image by a convex lens when an object is placed in front of the lens between its optical centre and principal focus.

(b) In the above ray diagram, mark the object distance (u) and the image distance (v) with their proper signs (+ve or –ve as per the new Cartesian sign convention) and state how these distances are related to the focal length (f) of the convex lens in this case.

(c) Find the power of a convex lens which forms a real and inverted image of magnification –1 of an object placed at a distance of 20 cm from its optical centre.


A student places a candle flame at a distance of about 60 cm from a convex lens of focal length 10 cm and focuses the image of the flame on a screen. After that he gradually moves the flame towards the lens and each time focuses the image on the screen.  

(a) In which direction-toward or away from the lens, does he move the screen to focus the image?
(b) How does the size of the image change?
(c) How does the intensity of the image change as the flame moves towards the lens?
(d) Approximately for what distance between the flame and the lens, the image formed on the screen is inverted and of the same size?


Analyse the following observation table showing variation of image-distance (v) with object-distance (u) in case of a convex lens and answer the questions that follow without doing any calculations : 

S. No. Object-Distance
u (cm)
Image-Distance
v (cm)
1 –100 +25
2 –60 +30
3 –40 +40
4 –30 +60
5 –25 +100
6 –15 +120

(a) What is the focal length of the convex lens? Give reason to justify your answer.

(b) Write the serial number of the observation which is not correct. On what basis have you arrived at this conclusion?

(c) Select an appropriate scale and draw a ray diagram for the observation at S.No. 2. Also find the approximate value of magnification.
 


Complete the following table:

Instrument Number of Convex
Lenses
Use
Simple Microscope .............. ..............
Compound Microscope .............. ..............
Telescope .............. ..............

An object is placed at a distance equal to 2f in front of a convex lens. Draw a labelled ray diagram to show the formation of image. State two characteristics of the image formed.


A burning candle whose flame is 1.5 cm tall is placed at a certain distance in front of a convex lens. An image of candle flame is received on a white screen kept behind the lens. The image of flame also measures 1.5 cm. If is the focal length of convex lens, the candle is placed:

(a) at f
(b) between f and 2f
(c) at 2f
(d) beyond 2f


A convex lens of focal length 15 cm produces a magnification of +4. The object is placed:
(a) at a distance of 15 cm
(b) between 15 cm and 30 cm
(c) at less than 15 cm
(d) beyond 30 cm


The focal lengths of four convex lenses PQR and S are 20 cm, 15 cm, 5 cm and 10 cm, respectively. The lens having greatest power is :
(a) P
(b) Q
(c) R
(d) S


Show by a diagram the refraction of two light rays incident parallel to the principal axis on a convex lens by treating it as a combination of a glass block and two triangular glass prisms.


What are the three principal rays that are drawn to construct the ray diagram for the image formed by a lens? Draw diagrams to support your answer.


Study the following diagram :

state the three characteristics of the image.


A converging lens forms the image of an object placed in front of it, beyond 2F2 of the lens.

Draw a ray diagram to show the formation of image.


Where is the image formed?


The given below figure shows an object OA and its image IB formed by a lens

draw suitable rays to locate the lens and its focus.

 


State two applications of a convex lens.


A student focussed the image of a distant object using a device ‘X’ on a white screen ‘S’ as shown in the figure. If the distance of the screen from the device is 40 cm, select the correct statement about the device.

(A) The device X is a convex lens of focal length 20 cm.

(B) The device X is a concave mirror of focal length 40 cm.

(C) The device X is a convex mirror of radius of curvature 40 cm.

(D) The device X is a convex lens of focal length 40 cm.


Distinguish between:

Concave lens and Convex lens


i. Which type of microscope has the arrangement of lenses shown in the  adjoining figure?
ii. Label the figure correctly.
iii. Write the working of this microscope.
iv. Where does this microscope used?
v. Suggest a way to increase the efficiency of this microscope.


The image obtained while finding the focal length of convex lens is ....................


Observe the following figure and answer the questions.

a) Which optical instrument shows arrangement of lenses as shown in the figure?
b) Write in brief the working of this optical instrument.
c) How can we get different magnifications in this optical instrument?
d) Draw the figure again and labelled it properly


Yesh find out F1 and F2 of symmetric convex lens experimentally then which conclusion is true.


Observe the following figure and complete the table:

Points Answer
(i) Position of the object  
(ii) Position of the image  
(iii) Size of the image   
(iv) Nature of the image  

At what position a candle of length 3 cm be placed in front of a convex lens so that its image of length 6 cm be obtained on a screen placed at distance 30 cm behind the lens?

What is the focal length of lens in part (a)?


If an object is placed in front of a convex lens beyond 2F1, then what will be the position, relative size, and nature of an image which is formed? Explain with a ray diagram.


Rewrite the following statement by selecting the correct option:
The power of a convex lens is 2.5 dioptres. Its focal length is ______________.

State the position of object, position of image, nature of image when: Convex lens is used in cine projector.


Diagram shows an object AB placed on the principal axis B of a convex lens placed in air. F1 and F2 are the two foci of the lens.

(i) Copy the diagram:
Draw a ray of light starting from B and passing through O. Show the same ray after refraction by the lens. Draw another ray from B which passes through F2 after refraction by the lens. Locate the final image
(ii) Is the image real or virtual?


For a specific glass lens f = 0.5 m. This is the only information given to the student. Which type of lens is given to him and what is its power?


_______ times larger images can be obtained by using a simple microscope.


_______ is a combination of two convex lenses with small focal length.


Object at 2F1 of a convex lens : Image at 2F2 : : Object at F1 : _______


Simple microscope : Number of convex lens one : : compound microscope : _______


: Object near the lens : : ______ :


Find the odd one out and give its explanation.


Find the odd one out and give its explanation.


Write the name.

The lens used in simple microscope.


Write scientific reason.

Adults need bifocal lens spectacle.


Observe the given figure and answer the following questions.

  1. Where is the above type of lens construction used?
  2. What type of image is formed by an objective lens?
  3. What happens instead of placing at Fo if the object is placed in between O and Fo?

Differentiate convex lens and concave lens.


A convex lens of focal length 20 cm can produce a magnified virtual as well as real image. Is this a correct statement? If yes, where shall the object be placed in each case for obtaining these images?


  1. In which type of microscope do you find the lens arrangement as shown in the following diagram?
  2. Write about the working and the use of this microscope.

Distinguish between Concave lens and Convex lens.


Distinguish between:

Concave lens and Convex Lens


Distinguish between Concave lens and Convex Lens.


Distinguish between:

Concave lens and Convex Lens


Distinguish between:

Concave lens and Convex Lens


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