CBSE Important Questions Ch 4 Class 12 Physics 2025 PDF

Chapter Electricity Class 12 provides in-depth information about current electricity. The chapter also covers Ohm's law, electric current, resistivity, and other electrical components. It also covers the visualisation of resistors, batteries, and capacitors. Students must master this chapter to pass board exams and competitive exams like JEE and NEET. They must have a proper understanding of this chapter to score well in their exams. This article provides the most important questions that can help Class 12 students in preparing for their exams effectively.

Chapter 3 Current Electricity contains various topics that are asked every year in board examinations. In this Current Electricity Important Questions PDF, you are going to study various topics like Electric Current, Ohm's Law, and Mathematical Expression for Current Density, Resistance, Resistivity, Current Density, Limitations of Ohm's Law, Drift Velocity, etc.

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In the table given below, we have provided the links to Moving Charges and Magnetism Most Important Questions and Answers PDFs for Class 12 Physics Chapter 4. You can download them without having to share any login info.

Overview of the Chapter:

The chapter on Current Electricity in Class 12 Physics primarily deals with the following key concepts:

1. Electric Current

2. Ohm's Law

3. Resistivity and Conductivity

4. Combination of Resistors

5. Kirchhoff's Laws

6. Electric Power and Energy

7. Heating Effect of Current

8. Magnetic Effect of Current (related to current electricity)

These topics, if well understood, can help students solve a variety of conceptual and numerical problems that are necessary for both theoretical and practical examinations.

Important Questions on the Current Electricity 

This section will answer the most important questions of the Class 12 Current Electricity.

What is electric current? Discuss the SI unit of current and its dimensional formula.

Electric current is the flow of electric charges through a conductor. It is measured in amperes (A). Although conventional current flows from positive to negative, the actual flow of electrons flows in the opposite direction. The SI unit for electric current is ampere (A). The dimensional formula of current is [I] (where I represent the current).

Formula for Electric Current:

I = Q / t

Where:

• I denote electric current, expressed in amperes (A).
• Q represents the charge, given in coulombs (C).
• t stands for the time, in seconds (s).

Explain Ohm's Law. Derive it and explain its significance.

Ohm's law is one of the basic principles that link voltage (V), current (I), and resistance (R) with a simple formula. That is, the current passing through a conductor is directly proportional to the potential difference offered to it and inversely proportional to the resistance of that conductor.

Ohm's Law Formula: V = I. R

where V is the potential difference (voltage), I is the current, and R is the resistance. This law is useful for understanding the concept of electrical circuits.

What is the difference between series and parallel combinations of resistors? Derive the equivalent resistance for both cases.

Series Combination: If resistors are connected in a straight line along a single path, then they are said to be connected in series. In this connection, the sum of the individual resistances is equal to the total resistance R_t

Formula: 

R_t = R₁ + R₂ + R₃ + …

Where R₁, R₂, R_3, … denote the individual resistances of the resistors.

Parallel Combination: Resistors connected in parallel allow the current to have more than one path. The total resistance is less than that of any single resistor.

Formula: 

1 / Rt = 1 / R1 + 1 / R2 + 1 / R3 + …….

Where R1, R2, R3,…… represent the individual resistances.

What is electric power? Derive the relation between power, voltage, current, and resistance.

Power is defined as the rate at which an electrical device changes electrical energy into other forms, such as heat, light, or mechanical energy. Power is measured in watts (W).

Power Formula

P = V. I

Here,

• P is the power expressed in watts, W
• V is the potential difference that is measured in volts, V
• I is the current that is measured in amperes, A

An alternative method to calculate the expression of power is through resistance. This is by using the Ohm's law:

P = I². R = V² / R

Derive the expression for the resistance of a conductor in terms of its resistivity, length, and cross-sectional area.

Resistance is the opposition that the electric current offers while passing through a conductor. This is dependent on the material, length, and cross-sectional area of the conductor. Resistance is measured in ohms (Ω).

Resistance Formula:

R = ρ. L / A

Where:

• R is the resistance in ohms, Ω
• ρ is the resistivity of the material in ohm-meters, Ω⋅m
• L is the length of the conductor in meters, m
• A is the cross-sectional area of the conductor in square meters, m^2

Define resistivity and conductivity. How are these properties related to the material of a conductor?

Resistivity, represented by the symbol ρ, is a characteristic of a material that resists the flow of electric current. It is influenced by the type of material, its temperature, and its physical state. The standard unit of resistivity is ohm-meter (Ω·m). On the other hand, conductivity, denoted by σ, is the reciprocal of resistivity and measures how easily a material allows the flow of electric current. The relationship between resistivity and conductivity can be expressed as:

ρ = 1 / σ

Both resistivity and conductivity are affected by factors such as temperature and the presence of impurities in the material.

What is Joule’s Law? How does the heating effect of current work in resistors?

Joule's law explains that the heat (H) generated when an electric current passes through a resistor is directly proportional to the square of the current, the resistance, and the duration of the current flow:

H = I² . Rt

This heat generation is fundamental to devices such as electric heaters and is important for understanding energy losses in electrical circuits caused by resistance.

What is superconductivity? What are its applications?

Superconductivity refers to the ability of specific materials to show zero electrical resistance when they are cooled below a certain critical temperature. This phenomenon has various applications, including powerful electromagnets, medical imaging techniques like MRI, and efficient power transmission without losses.

What are the factors that affect the resistance of a conductor?

There are several reasons why a conductor is resistant. Some of these include:

• Material: Different materials have different resistivities. Conductors such as copper and aluminium have low resistance, while insulators such as rubber and wood have high resistance. 
• Length of the conductor: The resistance of a conductor is directly proportional to its length. The longer the conductor is in terms of length, the higher its resistance will be.
• Cross-sectional area: The cross-sectional area of the conductor is inversely proportional to its resistance. The wider the cross-sectional area, the less resistance it will carry.
• Temperature: Usually in materials, the resistance increases with temperature. Conversely, in some materials such as semiconductors, resistance decreases with temperature.

Numerical Problems

Given a network of resistors in series and parallel, calculate the equivalent resistance and the current flowing through the circuit when a potential difference is applied.

Calculate the electric power consumed by a device given its resistance and current or voltage.

The chapter on Current Electricity in Class 12 Physics is essential for understanding how electrical circuits operate and the principles that govern electric current and resistance. The questions explored in this article are important for both conceptual understanding and practical problem-solving skills. By focusing on these key questions, students can make sure they are thoroughly prepared for their exams and have a strong understanding of the concepts that form the basis of modern electrical and electronic technologies.