Electricity

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CURRENT ELECTRICITY

Charge

It is a fundamental property of an atom. It may be positive or negative.
Like charges repel each other and opposite charges attract.

SI unit of charge is coulomb. 1 Coulomb charge= Charge present on approx.

6 \times 1 0^{18}

electrons Charge on 1 electron

= 1.6 \times 1 0^{- 19}

C . The formula to determine the amount of charge is:

Q = n e

Where, Q = Charge(total), n = No. of electrons, e = Charge on 1 electron

Current

The current is defined as the rate of flow of charge through a particular conductor. The SI unit of current is Ampere (A). The device to measure current is Ammeter. The connection of an ammeter in an electric circuit is as shown below:

Important points to measure current:

Ammeter has low resistance and is always connected in series.
The direction of current is taken opposite to the flow of electrons as electrons.

Potential Difference

Potential Difference (V) is the work done to move a unit charge from one point to another. It is given by the formula:

V = \frac{W}{Q}

Definition of Volt

When 1 Joule work is done in carrying one Coulomb charge then the potential difference is 1 volt.
SI unit of Potential difference = Volt (V)

Ohm's Law

The potential difference across the two points of a metallic conductor is directly proportional to the current passing through the circuit provided that temperature remains constant.

Mathematical expression for Ohm's law:

I \propto V

I = \frac{V}{R}

R

is a constant called resistance for a given metal.

The V-I characteristics of an ohmic conductor:

Symbols of Some Commonly Used Components in Circuit

Resistors in Series

When two or more resistors are connected end to end, the arrangement is called a series combination.

Total/resultant/overall/effective resistance in series.

R_{e q} = R_{1} + R_{2} + R_{3}

Current through each resistor is the same.

Resistors in Parallel

In a parallel connection of resistors, all points on one side of the resistor are connected together and all points on the other side are connected together.

Total/resultant/overall/effective resistance in Parallel:

\frac{1}{R _{e q}} = \frac{1}{R _{1}} + \frac{1}{R _{2}} + \frac{1}{R _{3}}

The voltage across each resistor in a parallel circuit remains the same.

Electric Power

Electric power is the amount of electrical energy consumed per unit time. Amount of power consumed in a device is proportional to the current flowing in the device. The unit of electric power is watt.
Electrical power is given by:

P = V I = I^{2} R = \frac{V ^{2}}{R}

Heating Effect of Electric Circuit

Heat is produced inside a conductor due to the movement of the charged particles inside it. This heat produced is given by the formula shown below:

H = V I t = I^{2} R t = \frac{V ^{2} t}{R}