NCERT Solutions Class 12 Physics Chapter 4 Moving Charges and Magnetism

Chapter 4 Physics Class 12 Moving Charges and Magnetism explains concepts like a magnetic field, magnets, behaviour of charges, magnetic force and many others. This chapter will help students understand the science behind magnets and their functioning. The Class 12 Physics Chapter 4 NCERT Solutions is exclusively available for students appearing for CBSE exams and competitive exams like JEE or NEET. Every solution set consists of stepwise explanations in simple language that students can refer to for an easy read and thorough understanding. 

Key Topics Covered In NCERT Solutions Class 12 Physics Chapter 4

Here’s a detailed breakup of topics under NCERT Solutions Class 12 Physics Chapter 4

4.1 Introduction

The first topic under NCERT Solutions Class 12 Physics Chapter 4 is an introduction to the magnetic field. The magnetic field imposes a force on moving charges. Moving charges are perpendicular to the plane.  

4.2 Magnetic Force

The magnetic force is an effect of electromagnetic force and is one of the four fundamental forces of nature. This force results in the motion of charges. Any two objects containing a charge with the same direction of motion have a magnetic attraction force among them. Also, objects with charges moving in opposite directions have a repulsive force among them.

4.2.1 Sources and Fields

In this subunit of NCERT solutions class 12 Physics chapter 4.2, students will learn about the cause of magnetism. The motion of the electrical charge causes magnetism. Substances consist of atoms, which have protons, electrons and neutrons. The magnetic field describes the interaction between moving electric charges and magnetic materials. A charge moving in any magnetic field experiences a perpendicular force.

4.2.2 Lorentz Force

Lorentz forces the force exerted on a charged particle q moving with velocity v through an electric field E and magnetic field B. The electromagnetic force F on the charged particle is called the Lorentz force (after the Dutch physicist Hendrik A. Lorentz) and is given by F = QE + qv × B.

4.2.3 Magnetic forces on a current-carrying conductor

The NCERT solutions class 12 Physics chapter 4.2.3 explain magnetic forces. An electric current flowing via a conductor produces a magnetic field. The field exerts a force on a magnet located within the conductor’s area. The magnet additionally exerts an equal and opposite force at the current-carrying conductor.

4.3 Effect of Motion in a magnetic field

NCERT solutions class 12 Physics Chapter 4.3 describes the effects of motion in a magnetic field. The velocity component, perpendicular to the magnetic field, creates circular movement. In contrast, the velocity component, which is parallel to the field, moves the particle alongside a straight line. The pitch is the horizontal distance between consecutive circles. The ensuing motion is a spiral.

4.4 Effect of Motion in Combined Electric and Magnetic fields

When a moving charge comes under the effect of magnetic and electric fields, it experiences Lorentz force. Lorentz force is calculated as the vector sum of forces created by magnetic and electric fields. F = F(electric) + F(Magnetic) = q (E = v x B) 

Students may refer to NCERT solutions class 12 Physics chapter 4.4 to know more.

4.4.1 Velocity Selector

A Wien filter, also called a velocity selector, is a tool such as perpendicular electric or magnetic fields, used as a velocity filter for charged particles, as an example in electron microscopes and spectrometers. It is utilized in accelerator mass spectrometry to select particles based on their speed.

4.4.2 Cyclotron

NCERT solutions class 12 Physics chapter 4.4.2 describes cyclotron and its effects on the magnetic field. A cyclotron is a compact particle accelerator that produces radioactive isotopes used for imaging procedures. Stable, non-radioactive isotopes are positioned into the cyclotron, which accelerates charged particles (protons) to excessive energy in a magnetic field.

4.5 Effect of Magnetic Field due to a current element, Biot-savant law

A small current-carrying conductor of length dl carrying a current I is an elementary source of a magnetic field. The force on some other comparable conductor can be expressed quite simply in phrases of magnetic field dB because of the first. The dependence of the magnetic field was first identified using Biot and Savart.

4.6 The Effect of Magnetic Field on the Axis Of A Circular Current Loop

In this section of NCERT solutions class 12 Physics chapter 4, students learn about the effect of the magnetic field on the axis of a circular current loop. Magnetic field dB at point P due to current element idl, making a right angle to the line joining point P and current element, will be given by Biot-Savart law as:

dB = (μo/4π)idl sin(90°)/r2 = (μo/4π)idl/r2

4.7 Ampere’s Circuital Law

NCERT solutions class 12 physics chapter 4.7 describes Ampere’s Law and Ampere’s Circuital Law.

Ampere’s law states that “The magnetic field produced by an electric current is proportional to the size of that electric current, given  that a constant of proportionality equal to the permeability of free space is defined.”

Ampere’s Circuital Law states that the line integral of the magnetic field surrounding the closed loop equals the number of times the algebraic sum of currents passing through the loop.

H.dL=Ienc

Suppose a conductor carries a current I, then the current flow generates a magnetic field surrounding the wire. The equation’s left side illustrates an imaginary path encircling the wire, and the magnetic field is added at every point.

Students may refer to NCERT solutions class 12 Physics Chapter 4.7 for more information on Ampere’s law.

4.8 The Solenoid and the Toroid

4.8.1 The solenoid

A coil of wire designed to generate a strong magnetic field inside the coil is referred to as a solenoid. Wrapping the same wire around a cylinder creates a strong magnetic field whilst an electric current is passed. The number of turns of a solenoid is denoted by N.

B=0NIl

Here, B=solenoid magnetic flux density

0=magnetic constant

N=number of turns

I=current

l=length of the solenoid

4.8.2 The Toroid

A toroid is a hollow circular ring in the shape of a doughnut, with many turns of enamelled wire, wound so close that there is little space between the two turns.

4.9 Two Parallel Currents & their forces

Suppose one Ampere of current passes through each of two parallel conductors of infinite length, separated by one meter in space free of other magnetic fields. It causes a force of exactly two × 10−7 N/m on each conductor. To know more, students may refer to NCERT Solutions Class 12 Physics Chapter 4.

4.10 Effect of Torque on Current Loop, Magnetic Dipole

A twisting force that causes the rotation of objects is called torque. The point where an object rotates is the axis of rotation. Students will learn about the effect of torque on current loop and magnetic dipole under NCERT solutions class 12 Physics chapter 4.10.

A magnetic dipole is generally a tiny magnet of microscopic to subatomic dimensions, equivalent to a flow of electric charge around a loop. Electrons are magnetic dipoles that circulate atomic nuclei; electrons spin on their axes and rotate positively charged atomic nuclei.

4.10.1 Torque on a rectangle-shaped current loop in a uniform magnetic field

qzIf a rectangular loop carrying a steady current is located in a uniform magnetic field, it will experience a torque. The total force on the loop will be zero. Students may refer to NCERT solutions class 12 Physics chapter 4.10.1 to know more. 

4.10.2 Effect of Circular current loop as a magnetic dipole

The field lines resemble that of a magnet. Hence, it behaves as a magnetic dipole. Its poles can be found from its field lines (Field lines go away from the magnet from the north pole and enter from the south pole).

4.10.3 Effect of the magnetic dipole moment of a revolving electron

The value of eh/4πm is referred to as the Bohr magneton. In addition to the magnetic moment, the electron possesses a magnetic moment because of its spin. The resultant magnetic moment can be stated as the vector sum of the orbital and spin magnetic moment.

4.11 The moving coil galvanometer

It is a device used to measure electric currents. It is a sensitive electromagnetic device that may measure low currents even of the order of some microamperes. 

Students may click on the respective chapter names to access a more detailed NCERT solutions class 12 Physics chapter 4.

List of NCERT Solutions Class 12 Physics Chapter 4 Moving Charges and Magnetism

Students may click on the below links to view NCERT Solutions Class 12 Physics Chapter 4: 

• Chapter 4: Exercise 4.1 Solutions 
• Chapter 4: Exercise 4.2.1 Solutions
• Chapter 4: Exercise 4.2.2 Solutions 
• Chapter 4: Exercise 4.2.3 Solutions 
• Chapter 4: Exercise 4.3 Solutions 
• Chapter 4: Exercise 4.4.1 Solutions
• Chapter 4: Exercise 4.4.2 Solutions
• Chapter 4: Exercise 4.5 Solutions
• Chapter 4: Exercise 4.6 Solutions 
• Chapter 4: Exercise 4.7 Solutions
• Chapter 4: Exercise 4.8.1 Solutions
• Chapter 4: Exercise 4.8.2 Solutions 
• Chapter 4: Exercise 4.9 Solutions 
• Chapter 4: Exercise 4.10.1 Solutions 
• Chapter 4: Exercise 4.10.2 Solutions 
• Chapter 4: Exercise 4.10.3 Solutions 
• Chapter 4: Exercise 4.11 Solutions 

Students may click on the respective exercise of NCERT solutions class 12 Physics chapter 4 to access the solution provided by Extramarks. In addition, they can also access NCERT Solutions for different classes in the links below.

• NCERT Solutions Class 1
• NCERT Solutions Class 2
• NCERT Solutions Class 3
• NCERT Solutions Class 4
• NCERT Solutions Class 5
• NCERT Solutions Class 6
• NCERT Solutions Class 7
• NCERT Solutions Class 8
• NCERT Solutions Class 9
• NCERT Solutions Class 10
• NCERT Solutions Class 11
• NCERT Solutions Class 12

Key Features of NCERT Solutions Class 12 Physics Chapter 4

Physics Chapter 4 Class 12 covers information about the magnetic field, magnetic force, and charges’ behaviours. In exams, numerical problems may be asked from this section. All the NCERT solutions class 12 Physics chapter 4 comprise a detailed explanation with diagrams, graphs and derivations for formulae. Class 12 Physics Chapter 4 NCERT Solutions are prepared by Subject Experts at Extramarks. All solutions are in accordance with  CBSE guidelines, and every question is answered according to the weightage of marks.