**Ohm's Law** is one of the basic and important laws of electric circuits.

**Georg Simon Ohm ** was a German physicist and mathematician. As a school teacher, Ohm began his research with the new electrochemical cell, invented by Italian scientist Alessandro Volta. Using equipment of his own creation, Ohm found that there is a direct proportionality between the potential difference (voltage) applied across a conductor and the resultant electric current. This relationship is known as Ohm's law

Ohm’s law states that the voltage across any conductor is directly proportional to the current flowing through it. Assuming all the physical conditions and temperature remain constant.

Ohm’s law is valid only if the temperature provided and other physical factors remain constant.

**V = I * R **

In the above equation, the constant of proportionality, **R** is the Resistance and has units of ohms, with symbol **Ω**.

When the values of Voltage and Current are given, the formula for finding Resistance will be: ** R = V / I**

When the values of Voltage and Resistance are given, the formula for finding Current will be: ** I = V / R**

When the values of power and voltage are given, the formula for finding Current will be: ** I = P / V**

When the values of power and current are given, the formula for finding Voltage will be: ** V = P / I**

When the values of current and voltage are given, the formula for finding Power will be: ** P = V I**

When the values of current and Resistance are given, the formula for finding Power will be: ** P = I ^{2}R**

Where **I** is the current through the conductor in units of **Amperes**, **V** is the voltage measured across the conductor in units of **Volts**, **R** is the resistance of the conductor in units of **Ohms** and **P** is the Power dissipated in the conductor in units of **Watt**.

You can make use of the Ohm’s law triangle to remember the different equations of Ohm’s law that are used to solve for different unknowns(ie. V, I, R).

Experimental Verification of **Ohm’s Law**

Aim: To verify the Ohm's law.

Appartus Required:

- Resistors
- Ammeter
- Voltmeter
- Battery / Power Supply
- Switch
- Rheostat

**Procedure:**

1. The switch is closed in the first step and the rheostat is adjusted to get the minimum reading in the ammeter A and the voltmeter V.

2. The sliding terminal of the rheostat is then moved slowly to increase the current gradually and each time the value of current I flowing in the circuit and the value of potential difference V across the resistance is recorded. ie, different sets of values of V and I are recorded.

For each set of values of Voltage and Current, the ratio V / I is calculated using the below table.

The ratio of V / I gives a constant value called **R** which is called the resistance of the conductor.

Plot a graph between current and the potential difference (Voltage), it will be a straight line. With this we can conclude that the current is proportional to the potential difference.

Sl |
Voltage (V) |
Current (I) |
Calculated Resistance (R) |
---|---|---|---|

1 | |||

2 | |||

3 | |||

4 | |||

5 |