# power of convex lens is positive or negative

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## The power of convex lens is:

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Question

## The power of convex lens is:

**A**

## Negative

**B**

## Positive

**C**

## Zero

**D**

## Imaginary

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## Which type of lens has a a positive power, and b a negative power ?

Which type of lens has a a positive power, and b a negative power ?

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Which type of lens has a a positive power, and b a negative power ?

Question

Which type of lens has (a) a positive power, and (b) a negative power ?

Open in App Solution

The power of a lens is the measure of its ability to converge or diverge a parallel beam of light on refraction through it .Negative sign for Concave lens and Positive sign for Convex lens. The S.I.unit of power is dioptre (D).

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SIMILAR QUESTIONS

**Q.**Which type of lens has (a) a positive power, and (b) a negative power?

**Q.**The power of corrective lens used for which defect has a positive power?

**Q.**According to conventions, the power of corrective lens used for which defect has a positive power?

**Q.**Convex lens has positive power.

**Q.**In a Std. X class, out of

40 students, 10

students use spectacles,

2

students have positive power and

8

students have negative power of lenses in their spectacles.

Answer the following questions :

(i) What does the negative power indicate?

(ii) What does the positive power indicate?

(iii) Generally which type of spectacles do most of the students use?

(iv) What defect of eyesight do most of the students suffer from?

(v) Give two possible reasons for the above defect.

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## Which type of lens has negative power?A) Convex lensB) Concave lensC) Both A and BD) None

Which type of lens has negative power?A) Convex lensB) Concave lensC) Both A and BD) None. Ans: Hint: Reciprocal of focal length is considered as power of a lens. To the numerical value of power we assign negative and positive signs as per sign conve...

Which type of lens has negative power?A) Convex lens B) Concave lens C) Both A and B D) None Answer Verified 227.7k+ views 5 likes

**Hint:**Reciprocal of focal length is considered as power of a lens. To the numerical value of power we assign negative and positive signs as per sign convention. If the image resolves on the right side of the principal axis, the power is positive and if the image resolves on the left side of the principal axis, the power is positive.

**Formula used:**

P L = 1 f PL=1f Where P L PL

is the power of the lens.

f f is the focal length

**Complete step by step answer:**

Power of a lens is the ability to deviate the path of rays of light passing through it. If the lens converges the rays, power is positive and if the lens diverges the rays, the power is negative.

The converging and diverging abilities of both types of lenses is shown below,

So we can now have an idea that a convex lens has positive power and a concave lens has negative power.

**So, The correct answer is (B), concave lens.**

**Additional Information:**

We can also solve this question by considering the sign convention of geometric optics.

By sign convention, any distance measured from the principal of the lens in the left direction is negative and any distance measured from the right of the length is positive.

For a convex lens, focal length

(f) (f)

is positive and for a concave lens, the value of

f f is negative.

So by assigning signs to focal length in the power formula

( P L = 1 f ) (PL=1f)

we get negative value for concave lens and positive value for convex lens.

**Note:**Never mix up sign conventions in optics, because examiners tend to put the same numerical options with different signs to confuse a student. Quick trick is, anything up or right from the principal is positive and anything left or down from the principal is negative.

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