Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Class 10 Physics Solutions By Lakhmir Singh & Manjit Kaur

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Class 10 : Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

The document Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev is a part of the Class 10 Course Class 10 Physics Solutions By Lakhmir Singh & Manjit Kaur.
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Lakhmir Singh Physics Class 10 Solutions Page No:247

Question 15: A converging lens of focal length 5 cm is placed at a distance of 20 cm from a screen. How far from the lens should an object be placed so as to form its real image on the screen ?

Solution :

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Question 16: An object 5 cm high is held 25 cm away from a converging lens of focal length 10 cm. Find the position, size and nature of the image formed. Also draw the ray diagram.

Solution :

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Image is 16.6cm behind the oonvex lens.

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Image is 3.33 cm in size and Is real and inverted.

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Question 17: At what distance should an object be placed from a convex lens of focal length 18 cm to obtain an image at 24 cm from it on the other side ? What will be the magnification produced in this case ?

Solution :

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Question 18: An object 2 cm tall is placed on the axis of a convex lens of focal length 5 cm at a distance of 10 m from the optical centre of the lens. Find the nature, position and size of the image formed. Which case of image formation by convex lenses is illustrated by this example ?

Solution :

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
The image is formed 5.02cmbehind die convex lens and is real and inverted

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Since the object distance is much greater than the focal length, this example illustrates the case when the object is place

Question 19: The filament of a lamp is 80 cm from a screen and a converging lens forms an image of it on a screen, magnified three times. Find the distance of the lens from the filament and the focal length of the lens.

Solution : -u + v = 80cm------(1)
m = -3 (The image is real, since it firms en a screen) 
m = v/u = -3
v = -3u

Put in eq (1),
u = -3u = 80
-4u = 80
u = -20cm
Distance of lens from filament is 20cm.
v = -3u = 60cm 

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Question 20: An erect image 2.0 cm high is formed 12 cm from a lens, the object being 0.5 cm high. Find the focal length of the lens.

Solution : 

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Question 21: A convex lens of focal length 0.10 m is used to form a magnified image of an object of height 5 mm placed at a distance of 0.08 m from the lens. Calculate the position, nature and size of the image.

Solution :

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Image is formed 0.40 m in front of the convex lens.

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
h2 = 0.025m = 25mm
Size of image is 25 mm.
Image is virtual and erect

Question 22: A convex lens of focal length 6 cm is held 4 cm from a newspaper which has print 0.5 cm high. By calculation, determine the size and nature of the image produced.

Solution :

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Image is 1.5 cm high, virtual, erect and magnified.

Question 23: Determine how far an object must be placed in front of a converging lens of focal length 10 cm in order to produce an erect (upright) image of linear magnification 4.

Solution :

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

The object must be placed 7.5 cm in front of the converging lens.

Question 24: A lens of focal length 20 cm is used to produce a ten times magnified image of a film slide on a screen. How far must the slide be placed from the lens ?

Solution :

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Question 25: An object placed 4 cm in front of a converging lens produces a real image 12 cm from the lens.
 (a) What is the magnification of the image ?
 (b) What is the focal length of the lens ?
 (c) Draw a ray diagram to show the formation of image. Mark clearly F and 2F in the diagram.

Solution :

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Question 26: (a) An object 2 cm tall stands on the principal axis of a converging lens of focal length 8 cm. Find the position, nature and size of the image formed if the object is :
 (i) 12 cm from the lens
 (ii) 6 cm from the lens
 (b) State one practical application each of the use of such a lens with the object in position (i) and (ii).

Solution :

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Image is 24 cm behind the lens.
Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Image is 4 an high, real and inverted, 
Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Image is 24 cm in front of the lens
Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Image is 8 cm high, virtual and erect.
(b) (i) Used in film projectcr.
(ii) Used as a magnifying glass.

Question 27: (a) An object 3 cm high is placed 24 cm away from a convex lens of focal length 8 cm. Find by calculations, the position, height and nature of the image.
 (b) If the object is moved to a point only 3 cm away from the lens, what is the new position, height and nature of the image ?
 (c) Which of the above two cases illustrates the working of a magnifying glass ?

Solution :

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Image is formed 12 cm behind the lens.
Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Image is l.Scm high, rea! and inverted
Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Image is famed 4.8 an In front of ttie lens.
Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Image is 4.8cm high, virtual and erect

(c) Case (b)

Question 28: (a) Find the nature, position and magnification of the images formed by a convex lens of focal length 0.20 m if the object is placed at a distance of :
 (i) 0.50 m
 (ii) 0.25 m
 (iii) 0.15 m
 (b) Which of the above cases represents the use of convex lens in a film projector, in a camera, and as a magnifying glass ?

Solution :

Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Image is formed 0.33 m behind the lens
Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Image is formed 1 m behind tfie lens
Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Image is formed 0.60 m in front of die lens.
Solutions of Refraction of Light (Page No- 247) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Image is virtual and erect
(b) Film projector Case (ii)
Camera: Case (i)
Magnifying glass: Case (hi)

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