Where Must a Point Source of Light Be Placed in Front of a Convex Lens So as to Obtain a Parallel Beam of Light? - Physics

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One Line Answer

Where must a point source of light be placed in front of a convex lens so as to obtain a parallel beam of light?

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Solution

If the point source of light is placed at the 'first focal point' (i.e. the focal point on the left of the optical centreof the convex lens), then the rays of light after being refracted through the length obtain a parallel beam of light.

Concept: Convex Lens
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Chapter 5: Refraction through a Lens - Exercise 5 (B) 1 [Page 119]

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Selina Concise Physics Class 10 ICSE
Chapter 5 Refraction through a Lens
Exercise 5 (B) 1 | Q 3 | Page 119

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 image by a concave lens when an object is placed in front of it.

(b) In the above 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 concave lens in the case.

(c) Find the nature and power of a lens which forms a real and inverted image of magnification –1 at a distance of 40 cm from the optical centre.


If you focus the image of a distant object, whose shape is given below, on a screen using a convex lens, the shape of the image of this object on the screen would be:

(a)

(b)

(c)

(d)


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Instrument Number of Convex
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Telescope .............. ..............

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 am erect diminished image? 


An image formed on a screen is three times the size of the object. The object and screen are 80 cm apart when the image is sharply focussed. 

 State which type of lens is used. 


A convex lens of focal length 10 cm is placed in contact with a concave lens of focal length 20 cm. The focal length of this combination of lenses will be:
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(c) −10 cm
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Complete the following sentence:

A convex lens is placed in water. Its focal length will ……………………….


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Name a device in which this action of lens is used.


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.


A lens forms an inverted image of an object what is the nature of the image real or virtual?


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Distinguish between:

Concave lens and Convex lens


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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 ....................


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


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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  

Draw neat diagram to show the
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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.


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


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


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: Object near the lens : : ______ :


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Write scientific reason.

Adults need bifocal lens spectacle.


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  1. Where is the above type of lens construction used?
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Differentiate convex lens and concave lens.


  1. In which type of microscope do you find the lens arrangement as shown in the following diagram?
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OR

c. When a slide is placed 15 cm behind the lens in the projector, an image is formed 3 m in front of the lens. If the focal length of the lens is 14 cm, draw a ray diagram to show image formation. (not to scale)


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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