## Problem 30.7: Wheatstone bridge

Please wait for the animation to completely load.

The animation shows a "Wheatstone bridge," which is used to measure unknown resistors. Restart. Assume an ideal battery (no internal resistance) and ideal meters **(resistance is given in ohms, electric potential is given in volts, and current is given in milliamperes)**. Begin the animation (with unknown resistor A) to read the current on the ammeter. In a Wheatstone bridge you adjust the variable resistor until the ammeter reads 0 and then you can calculate the value of the unknown resistor.

- What is the unknown resistor in this case?
- Develop an algebraic expression for the unknown resistance as a function of R1, R2, and the variable resistor.
- Use your expression to quickly calculate unknown resistor B and unknown resistor C.

Problem authored by Anne J. Cox.