Question

A physics student is conducting an optical experiment using an Optical Bench Kit available in many physics classrooms. A lit candle is positioned 20.cm from a concave mirror that produces an image 12cm from the mirror. Calculate the image position if the candle is repositioned 30.cm from the mirror. A. 5.Ocm B. 7.5cm C. 10.cm OD. 11cm E. 15cm

Answer 1

Answer:

C) 10 cm

Explanation:

We shall first calculate the focal length of the mirror.

object distance u = 20 cm ( negative )

Image distance v = 12 cm ( negative )

using mirror formula

1/ v + 1 /u = 1/ f

-1/12  - 1/ 20 =1/ f

f =- 7.5 cm

In the second case

u = - 30 cm

f = - 7.5 cm

i / v + 1 / u = 1 / f

1 / v - 1/30 = - 1/ 7.5

v = -10 cm

Answer is C that is 10 cm