1-23then we multiply both sides of the expression by R_{x} to separate it:For example, in figure 1-5, we know that R1 is 60 ohms, R2 is 100 ohms, and R3 is 200 ohms. Tofind the value of R_{x}, we can use our formula as follows:Use of ac BridgesA wide variety of ac bridge circuits (such as the Wheatstone) may be used for the precisionmeasurement of ac resistance, capacitance, and inductance. Let’s look at ac bridges in terms of functionsthey perform.RESISTANCE BRIDGE.—An ac signal generator, as shown in figure 1-6, is used as the source ofvoltage. Current from the generator passes through resistors R1 and R2, which are known as the ratioarms, and through R_{s} and R_{x}. Again, R_{x} is known as resistance. R_{s} has a standard value and replaces R3 infigure 1-6. When the voltage drops across R2 and R_{s} are equal, the voltage drops across R2 and R_{x} arealso equal; no difference of potential exists across the meter and no current flows through it. As wediscovered with the Wheatstone bridge, when no voltage appears across the meter, the following ratio istrue:Figure 1-6.—Resistance bridge (ac).For example, if in figure 1-6 we know that R1 is 20 ohms, R2 is 40 ohms, and R_{s} is 60 ohms, we canfind the value of R_{x} using our formula as follows:

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