Current Electricity Chapter 3 Class 12 Physics – Notes, PDF, Solved Questions

current electricity

CURRENT ELECTRICITY – CBSE Class 12 Physics Chapter 3 Summary and a detailed description of the chapter and the definitions are provided to you. Also, the summary is followed by some extra questions from the chapter. There are answers provided after the summary for your easy revision. CURRENT ELECTRICITY – CBSE questions have also been solved by us.

Class 12 Physics Chapter 3 Current Electricity Notes 

Here, we have tried to give you a simple summary with some extra questions from Class 12 Physics Chapter 3 – Current Electricity. After that, you can also go through some extra questions from chapter 3. 


Let’s discuss all about flow of current and some equations which used to detect and find amount of total flow of current in any body.

Electric Current

  • Electric current is defined as a flow of electric charge.
  • It is measured as the rate of flow of charge. It means how much charge is flowing with respect to time.
    • For example, consider a charge of 20Coulomb flowing per second. Then the current will be 20Coulomb/sec.
  • Electric current is denoted by I. 
  • It is written as I=dQ/dT, where dQ is the rate of change of charge with respect to time.
  • I unit is Amperes (A).
    • The direction of current determines from where the current originated and where it will terminate.
    • It can be categorized into 2 ways:-Electronic and Conventional Currents.

Ohm’s Law

Ohm’s law states the relationship between electric current and potential difference. The current that flows through most conductors is directly proportional to the voltage applied to it. Georg Simon Ohm, a German physicist was the first to verify Ohm’s law experimentally.

Ohm’s Law Explanation

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

Mathematically, this current-voltage relationship is written as,

V = IR

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

The same formula can be rewritten in order to calculate the current and resistance respectively as follows:

I = V/R or R = V/I

Ohm’s law only holds true if the provided temperature and the other physical factors remain constant. In certain components, increasing the current raises the temperature. An example of this is the filament of a light bulb, in which the temperature rises as the current is increased. In this case, Ohm’s law cannot be applied. The lightbulb filament violates Ohm’s Law.

Electrical Resistance

The electrical resistance of an object is a measure of its opposition to the flow of electric current. Objects made of electrical insulators like rubber tend to have very high resistance and low conductivity, while objects made of electrical conductors like metals tend to have very low resistance and high conductivity.

Current Density, Conductance and Electrical Conductivity

Current density at a point in a conductor is defined as the amount of current flowing per unit area of the conductor around that point provided the area is held in a direction normal to the current. The unit of electrical conductivity is mho m-1 or siemens/m.

Current density (J): The electric current per unit area is called current density. Conductivity (σ): The property of a conductor due to which the current flows through it is called the conductivity of that conductor.

Combination of Resistors

In a series circuit, the output current of the first resistor flows into the input of the second resistor; therefore, the current is the same in each resistor. In a parallel circuit, all of the resistor’s leads on one side of the resistors are connected together and all the leads on the other side are connected together.

The main differences between resistance in parallel and resistance in series has been discussed in detail with the help of equations. After going through this part, students will be able to revise crucial concepts such as the following:

  1. In the case of resistance in series, the voltage of a resistor will be directly proportional to the resistance offered by the same

  2. Every resistor carries the same amount of current.

  3. In the case of parallel resistance, a current passing through each resistor will be inversely proportional to the resistance offered.


The resistivity of a material of a conductor is given by

ρ = m / n2 τ

where n = number of free electrons per unit volume.

The resistivity of a material depends on the temperature and nature of the material.

It is independent of dimensions of the conductor, i.e., length, area of cross-section etc.

The resistivity of metals increases with an increase in temperature as

ρt = ρo (1 + αt)

where ρo and ρt are resistivity of metals at O°C and t°C and α temperature coefficient of resistivity of the material.

For metals α is positive, for some alloys like nichrome, manganin and constantan, α is positive but very low.

For semiconductors and insulators. α is negative.

Resistivity is low for metals, more for semiconductors and very high for alloys like nichrome, constantan etc.


If you are studying in Class 12 you can also check Class 12 NCERT Physics Solutions from here. This will help you to know the solutions for all subjects covered in Class 12th. You can click on the subject wise link to get the same. Class 12 Chapter-wise, detailed solutions to the questions of the NCERT textbooks are provided with the objective of helping you compare their answers with the sample answers.

Read more: Summary of The Third level chapter, class 12 English


In this section, we will let you know some of the important questions and answers that might help you in the exam.

  1. What is Ohm’s Law?

Answer: Ohm’s law states that the voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions and temperature remain constant. 

2. Does static electricity have a current?

Answer: Static electricity is an imbalance of electric charges within or on the surface of a material or between materials. Static electricity is named in contrast with current electricity, where the electric charge flows through an electrical conductor or space and transmits energy.

3. What are types of current?

Answer: There are two kinds of current electricity: direct current (DC) and alternating current (AC). With direct current, electrons move in one direction. Batteries produce direct current. In alternating current, electrons flow in both directions.

4. What is KCL and KVL?

Answer: Kirchhoff’s Laws are generally named KCL (Kirchhoff’s Current Law) and KVL (Kirchhoff’s Voltage Law). The KVL states that the algebraic sum of the voltage at node in a closed circuit is equal to zero.  But, in complex electrical circuits, we cannot use this law to calculate the voltage and current. 

 5. What is the difference between AC and DC?

Answer: Alternating Current (AC) is a type of electrical current, in which the direction of the flow of electrons switches back and forth at regular intervals or cycles. Direct current (DC) is an electrical current that flows consistently in one direction.
These are CURRENT ELECTRICITY Important Question Answers – that will help you to score better marks in the exams. Here we have provided you with all types of current electricity important question answers & extra solutions, it depends on your how-to catch-up lots of solutions and hard preparation for better performance in your results