Question

When an object is placed 10 cm in front of a certain mirror, a virtual image is formed 20 cm from the mirror What is the focal length of the mirror? -20 cm 0 +6.7 cm O +20 cm 0 -67 cm

Answer 1

`\huge\boxed{\sf f \approx 6.7 \ cm}`

Step-by-step explanation:

Given data:

Object distance = p = 10 cm

Image distance = q = 20 cm

Required:

Focal length = f = ?

Formula:

`\displaystyle (1)/(f) = (1)/(p) + (1)/(q)`

Solution:

Put the given data in the above formula.

`\displaystyle (1)/(f) = (1)/(10) + (1)/(20) \\\\(1)/(f) = 0.1 + 0.05\\\\(1)/(f) = 0.15\\\\f = 1 / 0.15\\\\f \approx 6.7 \ cm\\\\\rule[225]{225}{2}`