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A point object at a distance of 20cm from a thin plane convex lens of focal length 15cm (n=1.5) .Now the curved surface is silvered .If the image forms at a distance 24x /7cm from object towards lens then x is ???

A point object at a distance of 20cm from a thin plane convex lens of focal length 15cm (n=1.5) .Now the curved surface is silvered .If the image forms at a distance 24x /7cm from object towards lens then x is ???

Grade:11

4 Answers

Aman Bansal
592 Points
9 years ago

Dear Ranjita,

Lenses are found in a huge array of optical instruments, ranging from a simple magnifying glass to the eye to a camera’s zoom lens. In this section, we will use the law of refraction to explore the properties of lenses and how they form images.

The word lens derives from the Latin word for a lentil bean, the shape of which is similar to the convex lens in Figure 1. The convex lens shown has been shaped so that all light rays that enter it parallel to its axis cross one another at a single point on the opposite side of the lens. (The axis is defined to be a line normal to the lens at its center, as shown inFigure 1.) Such a lens is called a converging (or convex) lens for the converging effect it has on light rays. An expanded view of the path of one ray through the lens is shown, to illustrate how the ray changes direction both as it enters and as it leaves the lens. Since the index of refraction of the lens is greater than that of air, the ray moves towards the perpendicular as it enters and away from the perpendicular as it leaves. (This is in accordance with the law of refraction.) Due to the lens’s shape, light is thus bent toward the axis at both surfaces. The point at which the rays cross is defined to be the focal point F of the lens. The distance from the center of the lens to its focal point is defined to be the focal lengthf of the lens. Figure 2 shows how a converging lens, such as that in a magnifying glass, can converge the nearly parallel light rays from the sun to a small spot.

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Thanks

Aman Bansal

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Ranjita yadav
35 Points
9 years ago

Excuse me..Did u actly see what I asked ..?? Is it a joke..I din''t ask what is lens..I gave a full ques..n u r giving from where the word ''lens " derived..plzz ans.. if u know , don''t play a joke.!

Salim Shamim
37 Points
9 years ago

Dear Ranjita

 

When the surface is silver polished the lens would become a convex mirror and as it is given we have.

(1/image distance)+(1/object distance)=(1/focal length)

(1/image distance)+(1/20)=1/15

 

From here  IMAGE DISTANCE=  60cm and since its convex image is 

behind the mirror and virtual

now apparent distance of object from image=60+20=80cm 

as we have to go from object to mirror(20cm) then behind it(60cm).

now

24x/7=80

x=70/3.

 

HIT APRROVE PLEASE :)

Ranjita yadav
35 Points
9 years ago

The ans. is not corrct..ans is x=5

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