Current Electricity Class 12 Notes CBSE Physics Chapter 3 (Free PDF Download)

Section-A (1 Mark Questions)

1. What is the direction of the flow of current through electric circuit?

Ans. From high potential to low potential

2. A meter bridge is balanced with known resistance in the right gap and a metal wire in the left gap. If the metal wire is heated the balance point will shift to which side?

Ans. $\dfrac{V_{1}}{V_{2}}=\dfrac{l_{1}}{l_{2}}$

The resistance of the metal increases on heating

$\Rightarrow l_{2}^{'}> l_{1}$ 

∴ Balance point shifts towards right.

3. The potential difference across the terminals of a battery is 10V when there is a current of 3A in the battery from the negative to the positive terminal. When the current is 2A in the reverse direction, the potential difference becomes 15 V. Find the internal resistance of the battery.

Ans. E-3r=10 …(i)

E+3r=10 …(ii)

Solving these two equations we get $r=1\Omega$

4. A wire of resistivity ρ is stretched to double its length. What will be its new resistivity?

Ans. The resistivity remains the same as it does not depend upon the length of the wire.

5. What will happen to the relaxation time of electrons in a metal, if the temperature is changed?

Ans. The relaxation time of electrons decreases with the rise in temperature of the metal

6. Which physical quantity does the slope of voltage versus current graph for a metallic conductor represent? Give its SI unit.

Ans. The slope of voltage versus current graph for a metallic conductor represents resistance. It is measured in ohm.

7. Define drift velocity of electrons.

Ans. The mean velocity acquired by electrons in a conductor when an external electric field is applied to it is called drift velocity of electrons.

8. A resistance R is connected across a cell of emf ε and internal resistance r. A potentiometer now measures the potential difference between the terminals, of the cell as V. Write the expression for ‘r’ in terms of ε, V and R.

Ans. The required relation is $r=\left ( \dfrac{\varepsilon }{v}-1 \right )R$

9. A carbon resistor is marked in red, yellow, and orange bands. What is the approximate resistance of the resistor?

Ans. $24\times 10^{3}\Omega \pm20%$

10. Draw the graph showing the variation of conductivity with temperature for a metallic conductor?

Ans.

Section-B (2 Marks Questions)

11. If potential difference V applied across a conductor is increased to 2V, how will the drift velocity of the electron change?

Ans. $V_{d}=\dfrac{eE\tau }{m}$

$V_{d}=\dfrac{eV\tau }{lm}$

∴ Double the P.D. means drift velocity gets doubled.

12. Resistivities of copper, silver and manganin are $1\cdot 7\times 10^{-8}m$ , $1\cdot 0\times 10^{-8}m$ and $44\times 10^{-8}m$ . Respectively which of these is the best conductor? 

Ans. For a particular length and area of cross-section, the resistance is directly proportionate to, specific resistance. Therefore, silver is the best conductor because its specific resistance is less.

13. Name any one material having a small value of temperature coefficient of resistance. Write one use of this material?

Ans. Nichrome, an alloy has small value of temperature coefficient of resistance. It is used for making standard resistance coil.

14. Two wires A and B are of the same metal and of same length have their areas of cross section in the ratio 2:1 if the same potential difference is applied across each wire in turn, what will be the ratio of current flowing in A & B?

Ans. Since $R=\dfrac{1}{A}$

If area are in the ratio 2: 1 resistance will be in the ratio 1: 2.

And $I=\dfrac{V}{R}\Rightarrow I=\dfrac{1}{R}$ 

∴ Current will be in the ratio 2: 1

15. Calculate the equivalent resistance between points A and B in the figure given below.

Ans.

16.Under what conditions is heat produced in an electric circuit:

(i) directly proportional

(ii) inversely proportional to the resistance of the circuit

Ans. 

(i) If 1 in circuit is constant because $H=l^{2}Rt$

(ii) If V in circuit is constant because $H=\dfrac{V^{2}}{R}t$

PDF Summary - Class 12 Physics Current Electricity Notes (Chapter 3)

Current electricity is the branch of Physics that deals with the motion of charge, i.e., the dynamic state of charge. In our daily lives, there are various uses of current electricity such as: 

• A bulb glows when the charge passes through its filament.

• A computer turns ON only when the charge flows through its circuit.

All electric appliances, including those with batteries, like torches, are linked to the socket via a circuit or turned ON via an internal circuit.

The following are some of the subjects that were covered in the Current Electricity Class 12 Notes:

Electric Current

In this section, students will get a chance to revise the basic concepts regarding Electric current, which includes the definition and the equation. Furthermore, students will also be able to understand why electric current is a scalar quantity after reading through this part.

Current Carriers

Current carriers in different mediums like solids, gases and liquids have been discussed here. For instance, students will be able to understand how current flows in all these mediums.

Drift Velocity

The definition of drift velocity, along with its equation, has been explained in easy to understand language. Additionally, students can also go through concepts like relaxation time, the relation between current and drift velocity, mobility within this section of Current Electricity Class 12 Notes.

Ohm’s Law

This segment from Current Electricity Class 12 Notes will help a student to revise Ohm’s law which is one of the essential laws of Physics. The law states that potential difference across two ends of a conductor is directly proportional to the current flowing through it. Apart from that, this section of Physics Chapter 3 Class 12 Notes also show a step by step derivation of this law.

Electrical Resistance

Students will be able to revise various aspects of electrical resistance in this section. For instance, they will learn about terms like resistivity, conductance, conductivity, stretching of wire etc from this part of Ch 3 Physics Class 12 notes.

Current Density, Conductance and Electrical Conductivity

Students will come across concepts like conductors, insulators, semiconductors etc. in this segment. Additionally, this part also discusses how the resistance of metals increases with heat, while for insulators and semiconductors, it decreases with a rise in temperature. The functioning of a non-ohmic device has also been explained in this part within Current Electricity Class 12 Notes with the help of a diagram.

Colour Code for Carbon Resistors

A table has been given in this section of Current Electricity Class 12 Notes where different types of carbon resistors have been colour coded along with a letter. This will enable students to remember each resistor easily.

Combination of Resistors

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 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.

Students can go through Class 12 Physics Current Electricity Notes to review more fundamental concepts such as these.

Cell

In this notes of Physics Class 12 Chapter 3, students will study about cells or the device that converts chemical energy to produce electrical energy. Besides discussing terms like emf of a cell, potential difference, internal resistance, this section of Notes of Chapter Current Electricity Class 12 also contains graphs representing an electric cell in various positions.

Electric Current

Students can gain a clear understanding of the electric current and the subsequent equation representing the same. They will also be able to revise specific terms such as current due to transitory motion of charge, the rotatory motion of charge, current carriers etc. Moreover, graphical representation of various types of current has also been given in this section from current electricity Class 12 notes.

Kirchhoff’s Law

This law can be defined as the algebraic representation of a situation where current is meeting at a junction in a closed circuit. The sum of such current is zero.  Furthermore, students will also be able to revise how Kirchhoff’s first law supports the law of conservation of Charge and his second law supports the law of conservation of energy.

Heating Effect of Current

This section of Class 12 Physics Chapter 3 Current Electricity Notes discusses the heating effect of electric current through equations. To understand the equation, however, students will need to know some important terms and their relations with each other. This includes the following:

• Electrical power.

• Electrical energy.

• Consumption of electricity.

In Vedantu Notes of Ch 3 Physics Class 12, these terms have been explained clearly along with mathematical equations on the same.

Electrical Conducting Materials for Specific Use

Under this section of Class 12th Physics Chapter 3 Notes, materials that are used in electrical conducting have been discussed in detail. For instance, students will come to know that the filament in an electrical bulb is made up of tungsten. It is because this metal has a very high melting point. On the other hand, a fuse wire which is made up of tin-lead alloy has high resistance but a low melting point.

Superconductivity

In this section of Class 12 Physics Current Electricity Notes, students will learn how some metals and alloys can lose their resistance and become a superconductor. They will gain a better understanding of the process of superconductivity along with terms such as critical temperature. This section has also listed down some of the applications of superconductors that students can have a look through before examination.

Thus, students can download the Current Electricity Class 12 Notes to revise the critical concepts and score more in their Class 12 board examinations.

Revision Notes of Current Electricity and Its Key Points

Current electricity is considered one of the most important units of Physics for Class 12. It plays an important role in entrance examinations like JEE or NEET. Students who are appearing for these entrance exams can download the revision notes of Current Electricity for a last-minute quick revision. They can also go through the list of important formulas of current electricity of Class 12 curated by our subject-matter expert under the guidance of JEE/NEET teachers.

These revision notes are also beneficial for the students appearing in Board exams and looking for last-minute revision notes to clear their concepts.

Conclusion 

In Class 12 CBSE Physics, Chapter 3, you would typically cover concepts related to electric current, Ohm's law, resistors, electrical circuits, and their analysis. The chapter may also include topics such as Kirchhoff's laws, series and parallel combinations of resistors, and electrical measurements.

The conclusion of the chapter would summarise the key points covered in the chapter. It might emphasise the importance of understanding current electricity, its applications in daily life, and its relevance in various fields of science and technology. The conclusion may also highlight the need to master the fundamental concepts discussed in the chapter to effectively study advanced topics in physics.

To access the specific PDF notes for Class 12 CBSE Physics Chapter 3 on Current Electricity, I recommend checking Vedantu’s website or referring to your textbook, as they often provide downloadable resources for students.