Question

Find the power of the convex lens which forms real and inverted image of magnification-1 of an object placed at distance of 20 cm from the optic centre

Answer 1

Answer:

u= -20cm , m= -1 [given]

since magnification is given so, m=v/u

                                         implies v= mu

                                                        =( -1) * ( -20)

                                                         =20 cm

focal length(f)

1/f = 1/v - 1/u =1/20 - ( 1/-20) =1/10

implies, f = 10 cm

so, the power of convex lens= 1/f(in m) = 1/(10/100) = 100/10 = 10D

Answer 2

Answer:

• Power = 10 D

Explanation:

Given:

• Magnification = -1
• Object distance (u) = -20 cm

To Find:

• Power of the lens.

Now, first we will find image distance by magnification formula,

$\rm{\implies Magnification\;(m)=\dfrac{v}{u}}$

$\rm{\implies (-1)=\dfrac{v}{(-20)}}$

$\rm{\implies v=+20\;cm}$

Hence, image distance = 20 cm.

Now, we will calculate focal length of lens by lens formula,

$\rm{\implies \dfrac{1}{f}=\dfrac{1}{v} -\dfrac{1}{u}\;\;\;\;\;\;[Lens\;Formula]}$

$\rm{\implies \dfrac{1}{f}=\dfrac{1}{20}-\dfrac{1}{(-20)}}$

$\rm{\implies \dfrac{1}{f}=\dfrac{1}{20} +\dfrac{1}{20}}$

$\rm{\implies \dfrac{1}{f}=\dfrac{1+1}{20}}$

$\rm{\implies \dfrac{1}{f}=\dfrac{2}{20}}$

$\rm{\implies 2f=20}$

$\rm{\implies f=10\;cm}$

Hence, focal length = 10 cm = 0.1 m

Now, we will find power of convex lens by power of lens formula,

$\rm{\implies Power\;(P)=\dfrac{1}{f\;(In\;Meter)}}$

$\rm{\implies Power\;(P)=\dfrac{1}{0.1}}$

$\rm{\implies Power\;(P)=10\;D}$

Hence, Power of convex lens = 10 D.

#answerwithquality #BAL