Skip to Content Skip to Header Navigation

Mission RM7 Concave Mirror Mathematics

Getting your Trinity Audio player ready...

Hold down the T key for 3 seconds to activate the audio accessibility mode, at which point you can click the K key to pause and resume audio. Useful for the Check Your Understanding and See Answers.

 The Question

Jack and Jill are doing the 'Concave Mirror Lab.' They place a 4.5-cm high light bulb a distance of 17.9 cm from a concave mirror with a focal length of 13.6 cm. What would be the corresponding image distance for such an object location?

 Formula Fix

The mirror equation relates the object distance (do), the image distance (di) and the focal length (f):
 
1 / do + 1 / di = 1 / f

 Math Magic

The mirror equation, with its three reciprocal terms, is a little awkward to work with. It's recommended that you begin this problem by performing an algebra step to rearrange the equation such that the image distance (the unknown) is by itself on the left side of the equation. Then substitute the two numerical values into the equation and use your calculator to evaluate the right side. Once done, the reciprocal of the image distance is equal to the number on your calculator. Take the reciprocal of this number to determine the image distance.

 A Very Fine Detail

The Minds On Physics program calculates answers accurate to the fourth decimal place. Your answer does not need to be that accurate. The program will allow you to have a 1 percent deviation from the right answer without being wrong. This means two things: 1) Enter your answer with at least three significant digits. 2) Do not round any numbers until your final calculation.

Return to Screen Reader Navigation