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Visualize Alternatig Current (AC)


The electricity that we use in our houses flow in the form of alternating current (AC). The electricity we uses in torch is in the form of direct current (DC). In DC circuits, the current flows in one direction only. At any point, in the circuit, the current has a fixed direction. However, in AC, the current keeps changing its direction between two terminals. How many times does the current change its direction, that depends upon the source which generates the AC. The electricity that is generated in various power stations in India is at 50 Hz. So the AC that we use in our houses changes direction 100 times per second. This change is so rapid that we do not feel any discontinuity such as flickering of the bulb.


The objective is to visualize that current reverses its direction periodically in an AC circuit. For this, you need a low frequency oscillator, and a galvanometer.

Connect a galvanometer to the oscillator through a resistance. Keep the frequency at low value, 1 Hz or so. Look at the needle of the galvanometer.

The needle goes towards right and then come back towards left. This process keeps on repeating. Thus, the current keeps changing direction in the circuit. If we increase the frequency of oscillator, the needle oscillate faster. At certain stage (may be 10 Hz or so), the change become so fast that the galvanometer needle is not able to follow the change and hence stay almost at zero.

Variant: Diode Action

The objective of this demo is to show diode action. You need a low frequency oscillator, a diode, a resistor, and a sensitive galvanometer.

Connect the oscillator to a diode, a resistor and a galvanometer. Look at the needle of the galvanometer. From the middle, it goes to one side and returns to the middle. It does not go on the other side, stays in the middle for some time and again goes in the same direction. This keeps on continuing.

Stop the current, remove the diode, invert it physically and reconnect. Now, you see that the needle deflects in the opposite direction. It goes from the middle to that side and returns.

These observations shows that the diode allows the current to flow only in one direction and not in the opposite direction. Therefore, it acts as a half wave rectifier.


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