Question

A 2 cm high object is placed on the principal axis of a concave mirror at the distance of 12 cm from the pole if the image is inverted really and 5 cm high then the focal length of a concave mirror used is what is answer​

Answer 1

ANSWER :-

14 ) (b) 30 cm

15 ) (b) 8.6 cm

16 ) (c) 2.5

$\huge\mathfrak\red{question}$

A 2 cm high object is placed on the principal axis of a concave mirror at the distance of 12 cm from the pole if the image is inverted really and 5 cm high then the focal length of a concave mirror used

$\huge\mathfrak\green{to \: find}$

• magnification
• image distance
• focal length

$\huge\mathfrak\blue{solution}$

height of object = +2 cm

height of image = -5 cm [ - ve shows inverted]

$\boxed{magnification \: = \frac{image \:height }{object \: height} }$

$m \: = \: \frac{ - 5}{ + 2}$

$= - 2.5 \: cm \:$

image distance = v

object distance = u

$\boxed{m \: = \frac{ - v}{u } \: }$

object distance , u = -12 cm

magnification , m = -2.5

$- 2.5 \: = \frac{ - v}{ - 12}$

$- v \: = - 2.5 \times - 12$

$- v \: = 30 \\ v = - 30 \: cm$

$\boxed{mirror \: formula \: \frac{1}{f \:} = \frac{1}{u } + \frac{1}{v} }$

$\frac{1}{f} = \frac{1}{ - 30} + \frac{1}{ - 12}$

$\frac{1}{f} = \frac{ - 7}{60}$

$f \: = \frac{ - 60}{7}$

$= - 8.6 \: cm \:$