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Power of lens notes and numericals to practice
notes
power definition
capacity of lens to converge or diverge light rays passing through it
compulsory draw diagram
units are dioptres
formula
power =1/ f. in m. or 100/f in cm
I dioptre or define unit of power
1 diopter is power of lens whose focal length is 1 m or 100 cms
power of combination p= p1. + p2. + p3 ..........
power of convex. lens positive
power of concave lens is negative
numericals to practice
1.Two thin lense of power+3.5D and -2.5D are kept in contact.find the power and focal length of combination and its nature.
2.A convex lens of powerl length 25cm and concave lens of focal lenth 10cms are placed in contact what is nature ,power and focal length of combination
3.the power of combination of two lenses x and y is +5D.the focal lengtj of combination of lens x is 14cm.state the nature and focale length of lens y.
4.how are power and focal length of lenses are related.you are provided with two thin lenses of ficale length 20cm and 40 cm respectively.which lens will use to produce more convergent light.
5 a convex lens has focal length of 10cm.what is its power
6.A student uses lens of focal length 50 cm and another of -50 cm.what is the nature and its power used by each of them
7.two thin lenses of focal length +10cm and
-5cms are kept in contact with each other what is the focal length of its combination
8.power of combination of two lenses is +2.5 D and focal length of one is -20 cm what is foclalength and nature of other lens
9.fical length of combination of 2 lens is +20cm and power of one it is -5D find the power of other lens and its nature
10. three lenses of focal length are 10cm -20cm and -25cm.what is power of combination this 3 lenses
11.what happens if lens is dipped in water
ans.
When a lens is dipped in water its focal length increases
. Focal length is inversely proportional to magnification power (angular magnification), hence
power decrease
with the increasing wavelength.
12.what happens to focal length when mirror is dipped in water
ans.
no change it remains same
13.which has more focal length thin or thick lens
ans.
thin lens has more focal length
hence less power
as power is inversely proportional to focal length
14.the power if concave lens is 2.5 D .find the focal length of lens
15..find power of concave lens of focal length 2m
16..find the focal length of lens of power -2D.
17..two lenses of power +2.5 D and -0.5D aare kept in contact.what is the power of combination and focal length of combination.
18..two lenses of power +3.5D and - 2.5 D are placed in contact. what is power and focal length of combination
19.a convex and concave lens of focal length 50 cm and 40 cm.are placed in contact find power and focal length of combination
20. a combination of convex and concave lens has power +2 D.if the focal length of convex lens is 25 cm.find the focal length of concave lens used in the combination.
21.a convex lens has fl. 10cm.find the power
22.a student has lenses if fl +50cm and another of fl.-50 cms.what are nature of each and power of each lens.and power of combination
23.two thin lenses of fl.19cm and -5cm are kept in contact t.what is fl and power of combination.
24.you are given lenses with power 10D,5D,-20F,and -10D.taking a pair of lenses at a time.which two lenses will you select to have a combination of total fl. when the two lenses are kept in contacting each case.
a.20cm
b.-10cm
c.-20cm
d.20/3 cm.
25.power of lens is +4D.what kind of lens is it and find its fl
26.a lens has fl 10cm.what is the power of lens and its nature
27.the power of lens is-2D.what is its fl and nature
28.focal length of lens in photographic camera is 5cm.find the power of lens
29.two lenses of power 3D and -5D are kept in contact to form a composite lens.an object is kept at a distance of 50 cms from this composite lens.find the position of image
30..tow lenses of fl 10cm and -10cm respectively.find nature and power of both the lenses.which of this two lenses will form virtual and magnified image of an object placed at 8cm from the lens.draw ray diagram to justify your answer.
31.the power of lens is 5D.what is nature and fl of lens.where should object from this lens to be place to get image of same size.justify with ray daigram
32.how does the power of lens change if the fl is doubled.
33.which lens has more power thick or thin lens.
34.find the power of lens of concave lens of fl 20cm.
35.find the fl of convex lens is 25cm.express power with sign convention
36..(2020model paper)
Refractive index of water with respect to air is 1.33 and that of diamond is
2.42.
(i) In which medium does the light move faster, water or diamond?
(ii) What is the refractive index of diamond with respect to water?
1.Two thin lense of power+3.5D and -2.5D are kept in contact.find the power and focal length of combination and its nature.
37.A convex lens of focal length 25cm and concave lens of focal lenth 10cms are placed in contact what is nature ,power and focal length of combination
38..the power of combination of two lenses x and y is +5D.the focal lengtj of combination of lens x is 14cm.state the nature and focale length of lens y.
39..how are power and focal length of lenses are related.you are provided with two thin lenses of ficale length 20cm and 40 cm respectively.which lens will use to produce more convergent light.
40. a convex lens has focal length of 10cm.what is its power
41.A student uses lens of focal length 50 cm and another of -50 cm.what is the nature and its power used by each of them
42.two thin lenses of focal length +10cm and
-5cms are kept in contact with each other what is the focal length of its combination
43.power of combination of two lenses is +2.5 D and focal length of one is -20 cm what is foclalength and nature of other lens
44.fical length of combination of 2 lens is +20cm and power of one it is -5D find the power of other lens and its nature
45. three lenses of focal length are 10cm -20cm and -25cm.what is power of combination of this 3 lenses and also find its focal length of combination and also nature of combination
notes
power definition
capacity of lens to converge or diverge light rays passing through it
compulsory draw diagram
units are dioptres
formula
power =1/ f. in m. or 100/f in cm
I dioptre or define unit of power
1 diopter is power of lens whose focal length is 1 m or 100 cms
power of combination p= p1. + p2. + p3 ..........
power of convex. lens positive
power of concave lens is negative
numericals to practice
1.Two thin lense of power+3.5D and -2.5D are kept in contact.find the power and focal length of combination and its nature.
2.A convex lens of powerl length 25cm and concave lens of focal lenth 10cms are placed in contact what is nature ,power and focal length of combination
3.the power of combination of two lenses x and y is +5D.the focal lengtj of combination of lens x is 14cm.state the nature and focale length of lens y.
4.how are power and focal length of lenses are related.you are provided with two thin lenses of ficale length 20cm and 40 cm respectively.which lens will use to produce more convergent light.
5 a convex lens has focal length of 10cm.what is its power
6.A student uses lens of focal length 50 cm and another of -50 cm.what is the nature and its power used by each of them
7.two thin lenses of focal length +10cm and
-5cms are kept in contact with each other what is the focal length of its combination
8.power of combination of two lenses is +2.5 D and focal length of one is -20 cm what is foclalength and nature of other lens
9.fical length of combination of 2 lens is +20cm and power of one it is -5D find the power of other lens and its nature
10. three lenses of focal length are 10cm -20cm and -25cm.what is power of combination this 3 lenses
11.what happens if lens is dipped in water
ans.
When a lens is dipped in water its focal length increases
. Focal length is inversely proportional to magnification power (angular magnification), hence
power decrease
with the increasing wavelength.
12.what happens to focal length when mirror is dipped in water
ans.
no change it remains same
13.which has more focal length thin or thick lens
ans.
thin lens has more focal length
hence less power
as power is inversely proportional to focal length
14.the power if concave lens is 2.5 D .find the focal length of lens
15..find power of concave lens of focal length 2m
16..find the focal length of lens of power -2D.
17..two lenses of power +2.5 D and -0.5D aare kept in contact.what is the power of combination and focal length of combination.
18..two lenses of power +3.5D and - 2.5 D are placed in contact. what is power and focal length of combination
19.a convex and concave lens of focal length 50 cm and 40 cm.are placed in contact find power and focal length of combination
20. a combination of convex and concave lens has power +2 D.if the focal length of convex lens is 25 cm.find the focal length of concave lens used in the combination.
21.a convex lens has fl. 10cm.find the power
22.a student has lenses if fl +50cm and another of fl.-50 cms.what are nature of each and power of each lens.and power of combination
23.two thin lenses of fl.19cm and -5cm are kept in contact t.what is fl and power of combination.
24.you are given lenses with power 10D,5D,-20F,and -10D.taking a pair of lenses at a time.which two lenses will you select to have a combination of total fl. when the two lenses are kept in contacting each case.
a.20cm
b.-10cm
c.-20cm
d.20/3 cm.
25.power of lens is +4D.what kind of lens is it and find its fl
26.a lens has fl 10cm.what is the power of lens and its nature
27.the power of lens is-2D.what is its fl and nature
28.focal length of lens in photographic camera is 5cm.find the power of lens
29.two lenses of power 3D and -5D are kept in contact to form a composite lens.an object is kept at a distance of 50 cms from this composite lens.find the position of image
30..tow lenses of fl 10cm and -10cm respectively.find nature and power of both the lenses.which of this two lenses will form virtual and magnified image of an object placed at 8cm from the lens.draw ray diagram to justify your answer.
31.the power of lens is 5D.what is nature and fl of lens.where should object from this lens to be place to get image of same size.justify with ray daigram
32.how does the power of lens change if the fl is doubled.
33.which lens has more power thick or thin lens.
34.find the power of lens of concave lens of fl 20cm.
35.find the fl of convex lens is 25cm.express power with sign convention
36..(2020model paper)
Refractive index of water with respect to air is 1.33 and that of diamond is
2.42.
(i) In which medium does the light move faster, water or diamond?
(ii) What is the refractive index of diamond with respect to water?
1.Two thin lense of power+3.5D and -2.5D are kept in contact.find the power and focal length of combination and its nature.
37.A convex lens of focal length 25cm and concave lens of focal lenth 10cms are placed in contact what is nature ,power and focal length of combination
38..the power of combination of two lenses x and y is +5D.the focal lengtj of combination of lens x is 14cm.state the nature and focale length of lens y.
39..how are power and focal length of lenses are related.you are provided with two thin lenses of ficale length 20cm and 40 cm respectively.which lens will use to produce more convergent light.
40. a convex lens has focal length of 10cm.what is its power
41.A student uses lens of focal length 50 cm and another of -50 cm.what is the nature and its power used by each of them
42.two thin lenses of focal length +10cm and
-5cms are kept in contact with each other what is the focal length of its combination
43.power of combination of two lenses is +2.5 D and focal length of one is -20 cm what is foclalength and nature of other lens
44.fical length of combination of 2 lens is +20cm and power of one it is -5D find the power of other lens and its nature
45. three lenses of focal length are 10cm -20cm and -25cm.what is power of combination of this 3 lenses and also find its focal length of combination and also nature of combination
46.
thank u sir
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