Question

Focal length of convex mirror is 45 CM if image is 5 times magnified then object distance will be

Answer 1

• Answer:  Explanation:f=45 M=-v/u  5=-v/u  V=-5u  Now 1/v-1/u=1/f  1/-5u-1/u=1/f  1-5/5u=1/45  -4/5u=1/45  1/u=1/45*-5/4  1/u=-1/36  U=-36 Please mark the answer as brainliest please

Answer 2

Given:

Focal length of the convex mirror $=45cm$

Magnification $=5$

To find:

Object distance

Explanation:

• A convex mirror has the focus and the radius of the curvature on the right side of the lens. Hence, for a convex mirror only 2 ray diagrams are possible.

1. When object is placed at infinity : In this case, the rays coming from the object reflect through the mirror and meets or gets converged at the focus on right side of the mirror.
2. When object is placed between focus and pole of the mirror : In this case, the rays gets has to be extended backwards to meet between the pole and focus on the right side of the mirror

• From both the ray diagrams, we could infer that convex mirror always forms diminished images and thus, the as per the question, magnification of $+5$ in a convex mirror is not possible.
• Hence, the convex curvature could be a lens rather than a mirror.

Solution:

We know, that the focal length of the convex lens is always positive, hence,

$f=+45cm$

We also know, magnification of a mirror is given by

$m=\frac{v}{u}$

$5=\frac{v}{u}$

$v=5u$

We have, the lens formula, that is

$\frac{1}{v}- \frac{1}{u} =\frac{1}{f}$

Substituting the known values, we get

$\frac{1}{5u}- \frac{1}{u} =\frac{1}{45}$

$\frac{1-5}{5u}= \frac{1}{45}$

$u=-36cm$

Final answer:

Hence, the object is placed at a distance of 36 cm in front of the lens. OR

$u=-36cm$