Definition, Examples and Application of Alternating Current Circuit

Alternating Current Circuit – Definition, Examples and Applications – Most of the electrical energy used today is generated by electric generators in the form of alternating current. This alternating current can be generated by magnetic induction in an AC generator. Electric current and voltage always have a fixed value, do not change with time. This kind of electric current and voltage is called DC (Direct Current) current and voltage. While the electric current and voltage whose value always changes with time periodically are called alternating currents and voltages or AC (Alternating Current) currents and voltages.

Alternating Current Circuit - Definition, Examples and Applications

Alternating current in the world of electricity is widely used. Based on this understanding, it can be interpreted that alternating current is in the form of a wave. In many applications, the electrical voltage used is generated by the source in the form of a voltage that is sinusoidal with time. Likewise, in electronic circuits, this kind of voltage is widely used which is generated by insulators.

In an alternating current circuit, both the voltage and the current strength vary periodically. Therefore, for practical use, a fixed amount of alternating electricity is needed, namely the effective price. A sinusoidal alternating voltage, available from a variety of sources. Sources of alternating current are generally generated by power plants such as Hydro Power Plants, Steam Power Plants, Gas Power Plants, Wind Power Plants and Solar Power Plants.

Also Read: Alternating Current Circuit Questions and Answers [+Pembahasan]

A. Definition of Alternating Current

Alternating current is an electric current that reverses direction with a fixed frequency, so it is called AC (Alternating Current). In alternating current electricity, the emf and the current has more than one direction or the direction changes as a function of time. The source of alternating current is an alternating current generator. An alternating current generator consists of a rectangular circuit that is rotated in a magnetic field. Alternating current is distinguished between alternating current which has a sinusoidal function or graphic pattern and alternating current which is non-sinusoidal as shown in the figure:

alternating current circuit

The source of alternating current is an alternating current generator, an alternating current generator consists of a square coil which is rotated in a magnetic field. The electromotive force (EMF) generated by an alternating current generator changes periodically according to the sine or cosine function. This sinusoidal emf is produced by a coil which rotates at a constant angular speed.

C. Effective Price and Average Price

In alternating current electricity, the magnitude of the emf (Ԑ), potential difference (V) and current (I) always changes as a function of time. For that we need a quantity that is fixed, effective and average values ​​are not used, both for emf, potential difference and current. AC ammeters and AC volt meters can measure the effective value of alternating current and voltage. The effective value of alternating current and voltage is the strength of current and voltage which is considered equivalent to direct current and voltage which produces the same amount of energy when passing through a conductor in the same time.

Effective Price (root-mean-square, rms)

The effective current value (Ief = Irms) of alternating electric current is defined as equal to the average current which, at the same resistance and time interval, produces the same amount of electrical work.

Average price (average-value)

The average current value of alternating current electricity is defined as equal to the magnitude of the average current which in the same time interval transfers the same amount of charge.

C. Power in the circuit

If an inductor is powered by alternating electric current, a magnetic field will arise in the inductor. To generate this magnetic field, energy is needed which will then be distorted in the magnetic field. If the electric current is stopped, the magnetic field will disappear. Simultaneously, the energy stored in the magnetic field will turn back into electrical energy. Because the inductor is powered by alternating current, there will be periodic changes in energy from electric energy to magnetic fields and vice versa from magnetic fields to electrical energy.

The same thing can happen with capacitors. When a capacitance is connected to an electric voltage, an electric field is created inside the capacitor. To create this electric field, energy is needed from an electric voltage. If the voltage is disconnected, the electric field inside the capacitor will also dissipate and the energy stored in it will return to the circuit in the form of an instantaneous electric current.

Because the capacitor is connected to an alternating voltage, there will be a periodic energy change event. So a pure inductor and a pure capacitor in an alternating current circuit do not consume electrical energy because what actually happens is a repeated change in electrical energy from the magnetic field circuit or electric field.

D. Application in Daily Life


Tuning is one part of a radio that serves to select one of the transmitter frequencies in the air. The main component in this section is Varco (variable condensator). How to tuning select one frequency from radio transmitter? The trick is to use the principle of resonance. Do you know what resonance is? Resonance is the vibrating event of another object due to the vibration of an object even though the two objects are not in contact. Why is it vibrating? Because there is a similarity in frequency between the two objects. Based on the principle of resonance, the tuning circuit on a radio works.

When we turn the varco, we change the capacitance and inductance values ​​in the tuning circuit so that it produces a frequency that is the same as the frequency on one of the existing radio transmitters. For example, if we want to listen to a broadcast from a radio transmitter that works at a frequency of 97.9 MHz, we will rotate the varco so that the capacitance value and the inductance value are changed to produce a frequency of 97.9 MHz as well. Thus, we can listen to broadcasts from the radio transmitter. This is also what causes us to hear an unclear sound (such as a hissing sound because there are two transmitters whose frequencies are mixed) if there is no resonance between the frequency in the tuning circuit and the frequency of the radio transmitter that we hear.

To find out the resonant frequency, we can use the formula:

resonant frequency


  • Fr is the magnitude of the resonant frequency
  • L is the inductance value


Filter (Filter) in the wave rectifier (rectifier) ​​serves to obtain a unidirectional output voltage that is flat from the rectifier circuit. The purpose of rectification is to obtain direct current. In a rectifier, we don’t get pure direct current but a periodic current that changes, so this direct current contains an alternating current component. This variation in voltage is called voltage ripple. The voltage ripple in a full wave rectifier is smaller than the voltage ripple in a half wave rectifier. To further minimize this voltage ripple, a filter is used which is tasked with passing the unidirectional component and preventing alternating components.

Capacitor Filters. By adding a capacitor parallel to the load R in the half-wave rectifier circuit, the voltage ripple will be greatly suppressed. As we know, capacitors can store energy. When the source voltage increases, the capacitor will be charged until it reaches its maximum voltage. When the source voltage decreases, the capacitor will release its stored energy through the load (because at this time the diode is not conducting). Thus the load will still obtain energy flow even though the diode is not conducting. Furthermore, when the diode conducts again, the capacitor will be charged and this stored energy will be released again when the diode is not conducting; and so on. This kind of filter can of course also be used in full wave rectifiers. Capacitor Filter Circuit

  • low pass (low pass filter)

This circuit is used to pass low frequency signals and attenuate high frequency signals

  • High pass (high pass filter)

This circuit is used to pass high frequency signals and attenuate low frequency signals.

Transformer (transformer)

Transformer (transformer) is a device used to increase or decrease the alternating voltage (AC). The transformer consists of 3 main components, namely: the first coil (primary) which acts as an input, the second (secondary) coil which acts as the output, and an iron core which serves to strengthen the magnetic field produced. The working principle of a transformer is as follows. When the primary coil is connected to an alternating voltage source, changes in the electric current in the primary coil cause a changing magnetic field. The changing magnetic field is strengthened by the presence of an iron core and the iron core is delivered to the secondary coil, so that at the ends of the secondary coil there will be an induced emf. This effect is called mutual inductance (mutual inductance).

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