What is alternating current and direct current?

What is alternating current and direct current?

1. A direct current flows in one direction only in a circuit.
2. The magnitude Of a direct current may be
   (a) constant
   (b) changes with time
3. Figure shows the graph of current against time for some direct currents.
   
4. An alternating current flows to and fro in two opposite directions in a circuit.
5. Figure shows an alternating current with a constant magnitude of 3 A.
   
6. Figure shows an alternating current with a magnitude that changes with time.
   (a) The amplitude of the current or the peak current is I_p = 5 A
   (b) The time for one cycle is, T = 0.04 s
   (c) The frequency of the alternating current is given by:
   
7. Figure gives more examples of alternating currents.
   
8. An alternating current can flow through both a resistor and a capacitor whereas a direct current can flow through a resistor only.
   

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Alternating Current and Direct Current Experiment

Aim: To compare the output generated by a direct current source and an alternating current source.
Materials: Two 2.5 V bulbs, bulb holders
Apparatus: Battery holder with two dry cells, alternating current power supply, plug key switch, cathode ray oscilloscope (C.R.O.), connecting wires
Method:

1. The two circuits are set up as shown in Figure.
2. The settings of the cathode ray oscilloscope are adjusted to obtain a clear trace on the screen.
3. The traces formed by the output from the battery and the alternating current supply are observed and compared.
4. The trace displayed on the screen of the oscilloscopes are sketched.

Observation:Discussion:

1. The battery made up of two dry cells is a direct current source. The power supply connected to the mains supply delivers alternating current.
2. Both the bulbs are lighted up. Therefore direct current and alternating current can flow through the filament of a bulb and produce a heating effect.
3. The direct current flows in one direction only. The direction of the alternating current changes with time.
4. The magnitude of the direct current remains constant. The magnitude of the alternating current changes between zero and a maximum value.

Conclusion:
A direct current flows in one direction only but the direction of an alternating current changes with time.