RC/RL/LC Circuits

1. Using an Oscilloscope

1. Obtain an oscilloscope, a small light bulb (with resistance R of a few Ω), a switch, and a DC voltage supply (or alternatively a 1.5 V battery).
2. Connect the circuit as shown in Figure 4, with the switch open. The connections in this experiment can be made with cables, clamps, or banana plugs into receiving ports on the instruments.
3. Select the vertical scale of the oscilloscope to a range that is close to 1 V. Select the time scale of the oscilloscope to a range that is close to 1 s.
4. Close the switch (thus switching on the light bulb). Observe the light bulb as well as the trace ("waveform") on the oscilloscope screen. The oscilloscope, connected in parallel to the light bulb, will measure the voltage across the light bulb, and this voltage is proportional to the current through the light bulb.
5. Now open the switch again (thus switching off the light bulb). Again observe the light bulb as well as the trace ("waveform") on the oscilloscope screen.
6. Repeat the steps 1.4 and 1.5, if necessary.

Figure 4: Diagram showing a light bulb connected to a voltage supply with a switch. An oscilloscope is connected in parallel with the light bulb to measure its voltage (proportional to the current).

2. RL Circuit

1. Obtain an inductor with inductance L of 1 milliHenry (mH).
2. Connect the inductor in series to the light bulb (with the oscilloscope connected in parallel to the light bulb), and to the voltage supply with an open switch, as shown in Figure 5a.
3. Close the switch. Observe the light bulb as well as the waveform on the oscilloscope.
4. Open the switch. Obtain another light bulb (of the same kind as the first light bulb) and connect it in parallel with the first light bulb, as shown in Figure 5b.
5. Repeat step 2.3 (close the switch), and observe the light bulbs and oscilloscope.

Figure 5: Diagram showing an RL circuit, with one light bulb ( a) or two parallel light bulbs ( b) acting as the resistor (R). An oscilloscope is connected in parallel with the light bulb(s) to measure the voltage across the light bulb(s), proportional to the total current.

3. RC Circuit

1. Obtain a capacitor with capacitance of 1 Farad (F).
2. Connect the capacitor in series with the light bulb (which is connected in parallel to the oscilloscope), and together to the voltage supply with the open switch, as shown in Figure 6a. This corresponds to the similar circuit shown in Figure 5a connected in step 2.2, except with the inductor replaced by the capacitor.
3. Close the switch. Observe the light bulb as well as the waveform on the oscilloscope.
4. Open the switch. Connect the second light bulb in parallel with the first light bulb, as shown in Figure 6b.
5. Repeat step 3.3 (close the switch), and observe the light bulbs and oscilloscope.

Figure 6: Diagram showing a RC circuit, with one light bulb ( a) or two parallel light bulbs ( b) acting as the resistor (R). An oscilloscope is connected in parallel with the light bulb(s) to measure the voltage across the light bulb(s), proportional to the total current.

3. LC Circuit

1. Connect an 8 mH inductor in series with another open switch (switch #2) and together in parallel to a 10 µF capacitor, as shown in Figure 7. Close the switch #1 to have the capacitor charged. No light bulbs are used in this part of experiment.
2. Connect the oscilloscope in parallel with the capacitor, as shown in Figure 7.
3. Now open switch #1, then right away also close switch #2. Observe the oscilloscope.

Figure 7: Diagram showing an inductor (L) with a switch connected in parallel to a capacitor (C), which is part of a series RC circuit studied in Figure 6. The oscilloscope is now connected in parallel to the inductor to measure its voltage.