Question

. A concave lens forms the image of an object such that the distance between the object and image is
10cm and the magnification produced is 1/4. The focal length of the lens will be --X10 find
value.
11
3r​

Answer 1

Mark as BRAINLIEST answer

Answer:

\begin{lgathered}\text{Distance between object and mirror} = 10 \ cm\\Magification = \frac{\text{height of the image}}{\text{height of the object}}=\frac{v}{u}\\\\\\u-v = 10\\v = u - 10\\\\m = \frac{v}{u}=\\\frac{u-10}{u}= \frac{1}{4}\\4u - 40 = 10\\u = -\frac{40}{3}\\\\v = -\frac{10}{3}\\\\Now,Lens \ formula:\\\frac{1}{f}= \frac{3}{-10}-\frac{3}{-40}\\\\\frac{1}{f}= \frac{-9}{40}\\f = \frac{-40}{9}\\\boxed{\boxed{f = -4.4}}\end{lgathered}

Distance between object and mirror=10 cm

Magification=

height of the object

height of the image

=

u

v

u−v=10

v=u−10

m=

u

v

=

u

u−10

=

4

1

4u−40=10

u=−

3

40

v=−

3

10

Now,Lens formula:

f

1

=

−10

3

−

−40

3

f

1

=

40

−9

f=

9

−40

f=−4.4