Experiment no 4

AC Ohm’s Law

Carandang, Carmela Geraldine M. Date Performed: Jan 28, 2013

ACT- 2ndyear Date Submitted: Feb 4, 2013

Remarks:_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Engr. C.D. Sanchez

Instructor

II. Theoretical Discussion

Alternating currents and voltages

Figure 1 shows the plot of alternating voltage and alternating current as a function of time in a circuit that has only a resistor and a source of alternating current — an ac generator.

| | | | | | Figure 1 | Current and voltage from an ac source through a simple resistor. | | |

Because the voltage and current reach their maximum values at the same time, they are in phase. Ohm's law and the previous expressions for power are valid for this circuit if the root mean square (rms) of the voltage and the rms of the current, sometimes called the effective value, are used. These relationships are

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Ohm's law is expressed thus: VR = IR, where VR is the rms voltage across the resistor and I is the rms in the circuit.

Resistor-capacitor circuits

A circuit with a resistor, a capacitor, and an ac generator is called an RC circuit. A capacitor is basically a set of conducting plates separated by an insulator; thus, a steady current cannot pass through the capacitor. A time-varying current can add or remove charges from the capacitor plates. A simple circuit for charging a capacitor is shown in Figure 2 .

| | | | | | Figure 2 | An RC circuit for charging a capacitor. | | |

Initially, at time t = 0, the switch (S) is open, and there is no charge on the capacitor. When the switch is closed, a current will pass through the resistor and charge the capacitor. The current will cease