Ohm's Law

Grouping of Cells

Kirchhoff's Law

Electric current is the

In most DC electric circuits, it can be assumed that the resistance to current flow is a constant so that the current in the circuit is related to voltage and resistance by Ohm's law. The standard abbreviations for the units are

The unit of electric charge is the

In current electricity, dry cells or secondary cells or generators are employed to create a potential difference in order to cause an electric flow in closed circuits just as a water pump is used to create pressure difference in order to drive water in water pipes. The unit of potential difference is

The electrical resistance of a circuit component or device is defined as the ratio
of the voltage applied to the electric current whichflows through it:

where,

**R** = resistance (ohm)

**V** = voltage (V)

**I** = current (A)

## Ohm's Law

It is the most fundamental law of electricity and was given by** George Simon Ohm ** 1828.
**Statement** : The current which flows in a conductor is proportional to the potential difference
which causes its flow provided the temperature of the conductor is constant.
## V = IR

where constant R is the resistance of the conductor. In this Ohm's law relation,**V** is in volt, **I** is in amperes and **R** is in ohms.

where,

It is the most fundamental law of electricity and was given by

where constant R is the resistance of the conductor. In this Ohm's law relation,

The series circuit is one in which the same current flows in all the components of the circuit.
If resistors R_{1}, R_{2}, R_{3} .... are connected in series, the equivalent
resistance of the combination is the **sum of the resistance** so connected.

## R = R_{1} + R_{2} + R_{3}

**
**##
Resistors In Parallel

A parallel circuit of resistor is one in which the same voltage is applied across all the components .
If resistors R_{1}, R_{2}, R_{3} .... are connected in parallel, then reciprocal
of the equivalent resistance is the ** sum of the reciprocals of the resistance** of seperate components.

The resistance of a conductor is found to be directly proportional to its

to its

where is a constant called the resistivity or specific resistance of the material of the wire.

The unit of resistivity is

There are generally three types of groupings of the cells:

To study complicated circuits containing more than one source of emf, Kirchhoff put forward
the following two laws in **1842**.

Before going to the Kirchhoff’s laws, let us first define two terms. A**node** in a network is a
point where three or more conductors are joined. A **loop** is any closed conducting path.

##
(i) First Law or Current Law

It states, “In any electrical network, the**algebraic sum of currents meeting at a point (or junction) is zero,** .”
The total current flowing towards a node (junction) is equal to the total current flowing away from that node,
i.e. the algebraic sum of the currents meeting at a node is zero. The first law is simply a statement
of the **conservation of charge** .

**
**##
(ii) Second law or Mesh law or Voltage law

It states, “In a closed circuit, the**algebraic sum of the products of the current**
and the **resistance** in each of the conductors in any closed path (or mesh) in a network
plus **sum of emfs** in that path is equal to zero.”

Before going to the Kirchhoff’s laws, let us first define two terms. A

It states, “In any electrical network, the

It states, “In a closed circuit, the

Resistors are colour coded in order to find their resistance easily.

For measurement of a resistance, a network made up of four resistance arms P,Q,R
and S is arranged

as shown. Arms AB and BC having resistances P and Q respectively are known as** ratio
arms** .

A galvanometer G is connected across B and D. A battery is connected across A and C. When the values of resistances P, Q, R and S are such that no current flows through the galvanometer G the bridge is said to be**balanced** . In that case B and D are at
the** same potential** and we have the condition

Usually**S** is an unknown resistance and P, Q and R are known.

as shown. Arms AB and BC having resistances P and Q respectively are known as

A galvanometer G is connected across B and D. A battery is connected across A and C. When the values of resistances P, Q, R and S are such that no current flows through the galvanometer G the bridge is said to be

Usually