 ## Introduction on AC Circuit

Subject: Physics

#### Overview

The current or e.m.f., whose magnitude changes with time and direction reverses periodically is known as alternating current or e.m.f. This note provides us an information about alternating circuits.
##### Introduction on AC Circuit

When a battery is connected to a circuit, the current flows steadily in one direction. It is called a direct current. Electric generators at electric power plants, however, produce alternating current due to many technical reasons. Alternating current results when a sinusoidal e.m.f or voltage is applied in a circuit. Circuits fed by the alternating source are known as A.C. circuits. Alternating current (AC) circuits carry energy due to the coordinated vibrations of neighboring electrons. While DC circuits require single electrons to (slowly) move through the circuit and carry energy thanks to the kinetic energy carried by electrons as they drift through the wire, AC manages to carry energy without any overall motion of the electrons through the circuit.

#### Alternating Current and E.M.F

The current or e.m.f., whose magnitude changes with time and direction reverses periodically is known as alternating current or e.m.f.

The instantaneous values of alternating current and e.m.f at any time t are given by  \begin{align*} I &= I_0 \sin \omega t \dots (i) \\ E &= E_0 \sin \omega t \dots (ii) \end{align*}

where I0 and E0 are their maximum value or peak value or amplitude of current and e.m.f respectively. Their angular frequency is called driving frequency and is given by

$$\omega = \frac {2\pi }{T} = 2\pi f$$

Where T is time period and f is frequency of alternating current or e.m.f.

1. Generation, transmission, and distribution of A.C. are more economical than that of D.C.
2. AC is easily convertible into D.C.
3. AC can be better controlled without any loss of electric power by using a choke coil.
4. The alternating high voltage can be stepped down or stepped up easily by using a transformer.
5. AC. can reach distant places without much loss of electric power by using a transformer.
6. AC. machines are easier to use.

1. C. cannot be used in the electrolysis process such as electroplating, electrotyping, and electrorefining etc. where only D.C. is used.
2. C. can be more dangerous than D.C. in terms of its attractive nature and also because its maximum value is $\sqrt 2$ times its effective value.
3. C. in a wire is not uniformly distributed through its cross-section. The a.c. density is much greater near the surface of the wire than that inside the wire. The a.c. density is much greater near the surface of the wire than that inside the wire. The concentration of a.c. near the surface of the wire is called the skin effect.
4. Markings on the scales of A.C. meters are not equidistant for small measurement

Reference

Manu Kumar Khatry, Manoj Kumar Thapa, Bhesha Raj Adhikari, Arjun Kumar Gautam, Parashu Ram Poudel.Principle of Physics. Kathmandu: Ayam publication PVT LTD, 2010.

S.K. Gautam, J.M. Pradhan. A text Book of Physics. Kathmandu: Surya Publication, 2003.

##### Things to remember

When a battery is connected to a circuit, the current flows steadily in one direction. It is called a direct current.

Alternating current (AC) circuits carry energy due to the coordinated vibrations of neighboring electrons.

The current or e.m.f., whose magnitude changes with time and direction reverses periodically is known as alternating current or e.m.f.

AC can be better controlled without any loss of electric power by using a choke coil.

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