Ohm's Law: Overview, Questions, Preparation

Ohm’s law is described as the relation between the potential difference and electric current. The current flowing in the metal conductors is directly proportional to the voltage of the current. Ohm's law was discovered by a German physicist Georg Simon Ohm, and later, the law was named after him.

The relation between current and voltage is written as:

V = IR

Here, R is the Resistance,

V is the Voltage,

And I is the Current.

It can be rewritten as:

I = V / R

OR,

R = V / I

Ohm's law is stated true if the physical factors and the temperature remain constant. However, in some cases, if the temperature is increased, the current also increases.

Ohm's Law magic triangle shows the relation between current, voltage, and resistance in a triangular form, making it easy to derive the conclusions. If two sides of a triangle are given, finding the third side would be easy. Each side is marked as V, I and R respectively in random order.

The applications of Ohm’s Law are listed below:

1. Ohm's Law is used to determine the relationship between voltage, resistance, and current.
2. It is also used to sustain the desired temperature and voltage across the electric circuit.

3. Ohm’s law is used to divert the current from one source to another used in dc ammeter and dc shunts.

There are some limitations of Ohm’s law which are as follows:

1. Ohm's law is not applicable for the unilateral elements such as diodes and transistors because the flow of current in unilateral electric elements is in one direction. Look at the characteristic curve of a diode below:

2. For other non – linear electrical circuits like capacitance, resistance, etc., it is difficult to keep the voltage and current constant.

3. The relationship between voltage and current doesn’t hold as there can be more than one voltage value for the same current. It can be understood by looking at the following diagram:

Ohm’s Law for Class 12

The chapter 'Current Electricity' holds a significant weightage of 11 marks. It includes four questions in total, consisting of one objective type question of 1 mark, one very short question of 2 marks, one short question of 3 marks, and one important long question of 5 marks giving a total of 11 marks.

1) State the formula used for Ohm’s Law.

Answer – The formula used to calculate Ohm's law is V = IR.

2) Write one application of Ohm’s Law.

Answer – Ohm's Law is used to determine the relation between voltage, resistance, and current.

3) Illustrate a limitation of Ohm’s Law.

Answer – Ohm's law is not applicable for unilateral elements such as diodes and transistors because the flow of current in unilateral electric elements is in one direction. It can be shown below:

[Image courtesy: NCERT]