Question

Lenses are objects made of transparent materials such as glass, clear plastic that has curved surfaces. Diverging lenses are thicker at their edges than at their centres and make light rays passing through them spread out. Converging lenses are thicker in their middle than at their edges and make light rays passing through them focus at a point. These are used in spectacles to help people with poorvision see better. The converging lenses magnify by bending the rays of light that pass through them to meet t a point called focus. Thicker the converging lens is at its centre, the more it magnifies and closer the focus is to the lens.(1 x 4 = 4)(i) Lenses are objects made of transparent materials such as glass, clear plastic that has curved surfaces. Diverging lenses are thicker at their edges than at their centres and make light rays passing through them spread out. Converging lenses are thicker in their middle than at their edges and make light rays passing through them focus at a point. These are used in spectacles to help people with poorvision see better. The converging lenses magnify by bending the rays of light that pass through them to meet t a point called focus. Thicker the converging lens is at its centre, the more it magnifies and closer the focus is to the lens.(1 x 4 = 4)(i)Ravi uses two lenses A and B of same size and material as shown.In fig.P1and P1are the powers of A and B.(Also here as seenP1is thin and P2is a thick lens)An object is kept at the same distance from the lens between F and 2F of each lens on the principal axis in turn. Let I1and I2be the image formed by the two lenses respectively. (iii)If lens A above has a focal length of 50cm and lens B a focal length of 5cm then which lens would you prefer to use while reading small letters in a dictionaryout of lenses A and B.

Answer 1

Answer:

A thin lens has more focal length than a thick lens.

Explanation:

A thin lens has more focal length than the thick lens.

That's why $f_{1} > f_{2}$

Since power is inversely proportional to focal length, therefore,

$P_{2} > P_{1}$

If the focal length is given in meters (m), the power of the lens is measured in diopters (D), just as the unit of lens power in diopters. Another thing to keep in mind is that for a converging lens, the optical power is positive and for a diverging lens it is negative.

For example, if the focal length of the lens is 20 cm, we convert it to meters, we get 0.2 m. To find the power of this lens, take the inverse of 0.2 and we get 5. So the power of this particular lens is 5 D.

If you've read about the lens manufacturer's formula before, you'd realize that what we're calculating there is actually the power of the lens. This means you can calculate the lens power using the radii of curvature of the two surfaces and the refractive index of the lens material.

An important application of using the power of lenses is "Optometry". Optometrists prescribe corrective lenses (either convex or concave lenses) based on visual impairment. Your eye is basically a lens and sometimes you may have trouble seeing clearly. This can be corrected by wearing corrective lenses with the appropriate power.

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Answer 2

Answer:

Explanation:

Compared to a thick lens, a thin lens has a longer focal length.

Given that the relationship between power and focal length is inverse,

The lens's power is expressed in diopters (D), the same unit of lens power, whether the focal length is provided in metres (m). Another thing to keep in mind is that the optical power is positive for a converging lens and negative for a diverging lens.

For instance, if we translate 20 cm of the lens' focal length to metres, we obtain 0.2 m. Take the inverse of 0.2 to determine the power of this lens, which comes out to 5. Therefore, this particular lens has a 5 D power.

Having read,You would understand that we are actually calculating the lens's power there if you remembered anything about the lens manufacturer's formula from earlier. Thus, the curvature radii of the two surfaces and the lens material's refractive index can be used to calculate the lens power.

Optometry is a significant use of the power of lenses. Based on vision impairment, optometrists recommend corrective lenses (either convex or concave lenses). Since your eye is essentially a lens, you could occasionally experience vision problems. By using corrective lenses with the right power, this can be fixed.

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