#### • Class 11 Physics Demo

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# Difference between AC and DC Circuits

Alternating Current:
In alternating current the flow of electric charges reverses after a certain period. The period in which the current reverses can also be known as frequency of the current. This is mostly produced by generators where the polarity of the bushes reverses after certain period and hence the flow of the electrons also reverses.

Direct Current:
In direct current, the flow of electrons or electric charges does not reverses that is it remains in the same direction. The direct current is very stable however it is more dangerous than the AC. The DC is also produced by generator however the AC generated by the generator is smartly converted to the DC. In DC generators the bushes changes the polarity and also the circuitry which takes the charges from the bushes. This way the current always flows in one direction. The DC is also generated mostly from the batteries.

DC Circuits and AC circuits:
In DC circuits the voltage source is constant and hence a constant current flows through the circuit. Due to this fact the DC circuits has pure resistances.

To calculate current in DC circuits we require simple equation like:

I = $\frac{V}{R}$;

The voltage in the DC circuit is given by V and resistance is given by R and since both are constant so the DC is constant and is proportional to voltage V.

In AC circuits, the voltage source produces electric current with a certain frequency and hence the circuit is not pure resistive in nature, the circuit offers resistive as well as reactive impedance.  The impedance is the combination of resistance, inductance and capacitance.

To calculate current in AC circuits we require equation like;

I = $\frac{V}{(Impedance)}$;

Since in AC circuits the voltage source is not constant and hence the current is also not constant and varies in proportional to that of the voltage.

The voltage in the AC circuit is given by;

V = V0 sin wt;

Impedance = XR + XL + XC;

We can understand the difference between AC and DC circuits by example.

Ex. Find the current if the voltage source of 15 volts is connected to a resistance of 5 ohms?

Ans. From the question it is clear that the voltage source is constant and hence the current produced would be DC. Since V = 15 volts and R = 5 ohms so the current would be;

I = $\frac{15}{5}$;

I = 3 amperes.

Ex. Find the current if the voltage source of 15 volts with a frequency of 50 hertz is connected to a circuit which has an impedance of 5?

Ans. As from the question it is clear that the voltage source is not constant is varying with the frequency of 50 hz, so the current produced is also proportional to that of the voltage and is also varying. Now using the above equation we can write the AC as;

I = $\frac{15\sin (100\pi t)}{5}$

I = 3 sin(100 πt);