Electricity and Magnetism ** 5L20.19 ** AC Circuits

Resonance

Phase relationships and resonance in an RLC circuit

Equipment:

• PASCO PI-9587B fequency generator - shelf 8D
• Aerovox decade capacitance box - shelf 11B
• Sprague decade inductance box - shelf 11D
• 7.5-ohm resistor - shelf 11A
• 1-ohm resistor - shelf 11D
• oscilloscope - in front of shelf 13
• 5 banana-to-banana cables
• 2 scope cables, banana to BNC
• video camera and holder - file cabinet between shelves 3 and 4

Theory: In a series RLC circuit at resonance, the current will be maximized, and in phase with the voltage. At frequencies lower than the resonance frequency, the capacitor tends to dominate and the voltage lags the current; at higher frequencies the inductor tends to dominate and the voltage leads the current.

Description: Use the following settings for C and L: C = 0.04 microfarads; and L = 0.04 H. The resonance frequency is about 1300 Hz. At 1100 Hz the circuit is clearly capacitive, and at 1500 Hz it is clearly inductive. It's also easy to see that the current peaks, and is in phase with the voltage, at resonance.
In a small room, the students can view the scope directly. In a larger room, the video camera can show the scope screen on a TV monitor, or all 6 monitors in room 107.

Setup time: 20 minutes

References: (available in the demo room)