# at what distance should an object be placed from a convex lens of focal length 18cm

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## At what distance should an object be placed from a

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Asked on 18th Jan, 2021

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?

Class 10th Physics

Answered 8584 Views

**Solutions :**

Balendu Anand

Answered on 18th Jan, 2021

Given,

The focal length of a convex lens, = 18 cm.

Image distance, = 24 cm

Object distance,

To find- Magnification

Solution:

By using lens formula-

1 v − 1 u = 1 f 1v−1u=1f\rule0ex0ex

where, = image distance, = object distance, and f = focal length

Substituting the values of** f, v **and **u **we get,

1 24 − 1 u = 1 18

124−1u=118\rule0ex0ex

1 24 − 1 18 = 1 u

124−118=1u\rule0ex0ex

18 − 24 24 × 18 = 1 u

18−2424×18=1u\rule0ex0ex

6 24 × 18 = 1 u

624×18=1u\rule0ex0ex

1 4 × 18 = 1 u 14×18=1u\rule0ex0ex u = − 72 c m u=−72cm\rule0ex0ex

So, the object distance is** -72cm**.

The object should be placed at a distance of -72 cm from the lens.

Now, the equation for finding magnification of a lens can be given as-

m = v u m=vu\rule0ex0ex

Substituting the values in magnification formula we get-

m = 24 − 72 m=24−72\rule0ex0ex m = − 1 3 m=−13\rule0ex0ex

Hence, the magnification produced will be

**m** **=** **−** **1** **3** **m=−13\rule0ex0ex** 0

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

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

By using lens formulaEasy Open in App Solution Verified by Toppr v 1 − u 1 = f 1

where v=24cm ,f=18cm

24 1 − u 1 = 18 1

from this we get u=−72cm

magnification of lens is m=

u v m= −72 24 =− 3 1

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## 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 ?

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 ?

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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 ?

Question

Open in App Solution Here, f = 18 c m v = 24 c m Using lens formula, 1 v − 1 u = 1 f ⇒ 1 24 − 1 u = 1 18 ⇒ 1 u = 1 24 − 1 18 = − 1 72 ⇒ u = − 72 c m

So, the object should be placed at a distance 72 cm from the lens.

Now, m = v u = 24 − 72 = − 1 3 Suggest Corrections 9

SAME EXERCISE QUESTIONS

**Q.**

State and explain the New Cartesian Sign Convention for spherical lenses.

**Q.**

A convex lens produces a magnification of +5. The object is placed : (a) at focus (b) between f and 2f (c) at less than f (d) beyond 2f

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