Basic Aspects of Alternating current. (page 2)
What a diode does to an alternating current
- Remove one of the connections to the power supply.
- Attach a diode in the circuit going from the power supply through the resistor.
- Turn on the AC power supply.
- Reattach the leads from the oscilloscope to the ends of the resistor.
- Display the AC signal on the oscilloscope screen.
- Turn down the AC power supply.
- Remove the diode. Reverse the direction of the lead and reattach the diode in the circuit.
- With the AC power supply turned on, observe how the signal changes.
Building a transformer
- Wind the 2-foot section of wire around the nail. Leave approximately 6-inch lengths of wire at each end, with about ¾ of the insulation removed from the ends of the wire. Keep track of how many turns you apply.
- Do the same with the 4-foot section of wire. There should be twice as many turns on this section.
- Attach the positive and negative of an AC power supply to the two leads of the 2-foot section of wire. (We can call this the primary coil.)
- Attach the two ends of an AC voltmeter to the points of contact between the power supply and the 2-foot section of the transformer wire.
- Attach the other AC voltmeter to the two leads of the 4-foot section of wire. What do you read?
- If you have a DC power supply available, apply a similar voltage to the primary windings. How is the voltage of the secondary affected?
A 60-cycle AC signal is displayed on an oscilloscope with a full wavelength repeating every 0.017 seconds. An AC signal has the form shown in Figure 115-2.
Inserting the diode in the circuit results in only one-half of the waveform flowing in the circuit. This means only the positive (or negative) half of the cycle is displayed, as shown in Figure 115-3 for a diode placed in one direction, or as in Figure 115-4 for a diode placed in the other direction.
Why It Works
Alternating current is constantly changing direction.
A diode is a device that passes the current in only one direction.
A transformer changes the AC voltage of an incoming signal based on the ratio of turns between the input and output sides of a transformer. A transformer only lets AC current through, but it will not pass DC current.
The ratio of the primary (in) to the secondary (out) voltage of a transformer is the ratio of the turns of the secondary to the primary. This is given by the equation Vp/Vs = Np/Ns where V represents the voltage, N the number of windings, p the primary, and s the secondary windings.
Other Things to Try
If you don't have a stand-alone oscilloscope, here are some other options:
- Build an adapter for the sound card oscilloscope.
- Use an audible tone, such as from an electronic synthesizer keyboard, to produce a signal that is compatible with a sound card oscilloscope.
- You can also generate an AC signal using a magnet suspended by a spring over a coil. The signal can be monitored by a sound card oscilloscope or PASCO voltage sensor, and the effects of the diodes can be studied.
Alternating current consists of a flow of electrons continuously reversing direction. The voltage of a common form of AC follows the rising and falling pattern of a sine wave.
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