Moving Charges and Magnetism

Important Topics of Moving Charges and Magnetism

1. Magnetic Force

A charged particle is affected by a magnetic force either when it passes through a magnetic field or when it is on a conductor that carries an electric current. This force is proportional to the charge, particle velocity, strength of the magnetic field, and the angle between the velocity and the field. This topic describes the reasons why magnetic force is not exerted on stationary charges. The direction of the force is calculated by Fleming's left-hand rule. The motion of particles cannot be studied without understanding the magnetic force. This topic has a lot of questions that are common in exams.

2. Lorentz Force

Lorentz force refers to the amount of force exerted on a charged particle in the presence of an electric and a magnetic field. It is the resultant force of both electric force and magnetic force on the particle. This topic assists in the study of how charges move in combinations of fields. It is an important part of the comprehension of machines like velocity selectors. To solve related numerical problems, conceptual clarity is highly required.

3. Motion of a Charged Particle in a Magnetic Field

This topic explains how a charged particle moves in a magnetic field depending on the direction of its velocity. The particle can move either in a circular manner or helically. Formulas of the radius, time period, frequency and pitch are obtained. This is significant to the explanation of cyclotrons and mass spectrometers. This topic has numerical problems that are frequently asked in competitive exams.

4. Motion of a Charged Particle in Electric and Magnetic Fields

When the electric and magnetic fields are applied to a charged particle simultaneously, the motion becomes more complicated. This topic describes the phenomenon of crossed-field motion and velocity selection. It assists in the explanation of the possible separation of charged particles with respect to speed. The principle is a mixture of the concepts of electrostatics and magnetism. Numerical questions are used to assess both the conceptual and formulaic knowledge. It is a particularly significant topic of JEE and NEET.

5. Biot-Savart Law

The Biot-Savart law is a mathematical statement giving the magnetic field due to a tiny current element. It defines the dependence of the magnetic field on the current, distance and the conductor direction. This law is applied to determine the magnetic fields of simple current arrangements. It is the basis of numerous derivations of the magnetic field. One has to have conceptual knowledge of the nature of vectors.

6. Ampere's Circuital Law

Ampere's circuital law relates the magnetic field around a closed path to the current enclosed by that path. It especially comes in handy when computing magnetic fields under symmetric cases. This law streamlines the calculations of the magnetic fields of solenoids and straight conductors. To have the correct application of this law, it is important to understand symmetry. The weightage of this topic is high in exams.

7. Magnetic Field around a Solenoid

This topic explains the magnetic field produced inside and outside a long current-carrying solenoid. The topic describes the magnetic field inside and outside a long current-carrying solenoid. It demonstrates that there is almost a uniform magnetic field within a solenoid. The expression of the field is determined by using ampere law. Solenoids are significantly useful tools that are employed as electromagnets. This is a topic that has theoretical and practical implications.

8. Force Between Two Parallel Current-Carrying Conductors

This topic explains the force of attraction or repulsion between two parallel conductors carrying current. The force direction is determined by the direction of currents (opposing or in the same direction). This interaction leads to the formal definition of the ampere. It has historical importance in electromagnetism. Theoretical knowledge is significant in solving questions from this topic.

9. Torque on a Current Loop, Magnetic Dipole

Torque on a Current Loop and Magnetic Dipole is an explanation of the behaviour of a current-carrying loop in a magnetic field. In this subject, a current loop is regarded as a magnetic dipole, and the notion of magnetic dipole moment is provided to define its strength and orientation. It discusses the effect of the magnetic field on the loop, which is that the field creates a torque on the loop, and it will start turning to align itself with the field. It is the working concept of electric motors and is significant in the interaction of magnetic fields and current-carrying conductors.

10. The Moving Coil Galvanometer

A moving coil galvanometer is a sensitive electrical device applicable in the detection and measurement of very small electric currents. The principle, construction, and working of the galvanometer are described using this topic on the basis of the torque acting on a current-carrying coil in a magnetic field. It brings out the idea of the current sensitivity and the way the coil is deflected in relation to the current flowing through the coil. Knowing this topic is necessary to learning the operation of electrical measuring instruments and is the foundation upon which to turn a galvanometer into an ammeter and a voltmeter.

11. Conversion of a Galvanometer into an Ammeter and a Voltmeter

Conversion of a Galvanometer into an Ammeter and a Voltmeter is an explanation of how a sensitive moving coil galvanometer can be converted into an instrument that can measure large currents and potential differences. In this topic, the application of shunt resistance to convert a galvanometer into an ammeter and high series resistance to convert it into a voltmeter is presented. It pays attention to the principles of work, circuit arrangement and condition that are necessary to measure correctly. This topic is significant to understand the design and operation of useful electrical measuring instruments.

Related Topics,

Important Formulas of Moving Charges and Magnetism

Significant Formulas of Moving Charges and Magnetism give the mathematical relationships required to examine the magnetic effects of moving charges and current-carrying conductors. These equations help students to determine the force of magnetism, the movement of a particle, a magnetic field, torque, and the behaviour of instruments precisely. These types of formulas should be revised and used regularly to be able to solve numerical problems with confidence in Class 12 board exams and in competitive exams such as JEE Main and NEET.

1. Magnetic Force:

• Magnetic force on a moving charge

$
\begin{aligned}
\vec{F} & =q(\vec{v} \times \vec{B}) \\
F & =q v B \sin \theta
\end{aligned}
$

• Magnetic force on a current-carrying conductor

$
F=B I l \sin \theta
$

2. Lorentz Force:

$\vec{F}=q(\vec{E}+\vec{v} \times \vec{B})$

3. Motion of a Charged Particle in a Magnetic Field:

• Radius of circular path

$
r=\frac{m v}{q B}
$

• Time period of circular motion

$
T=\frac{2 \pi m}{q B}
$

• Frequency (cyclotron frequency)

$
f=\frac{q B}{2 \pi m}
$

• Pitch of helical path

$
\text { Pitch }=v_{\|} T
$

4. Velocity Selector:

• Condition for undeflected motion

  $
  v=\frac{E}{B}
  $

5. Biot–Savart Law:

• Magnetic field due to a current element

  $
  d \vec{B}=\frac{\mu_0}{4 \pi} \frac{I(d \vec{l} \times \hat{r})}{r^2}
  $

6. Magnetic Field Due to Current-Carrying Conductors:

• Long straight conductor

$
B=\frac{\mu_0 I}{2 \pi r}
$

• Circular current loop (at centre)

$
B=\frac{\mu_0 I}{2 R}
$

• Magnetic field on the axis of a circular loop

$
B=\frac{\mu_0 I R^2}{2\left(R^2+x^2\right)^{3 / 2}}
$

7. Ampere’s Circuital Law:

$\oint \vec{B} \cdot d \vec{l}=\mu_0 I_{\mathrm{enc}}$

8. Magnetic Field Due to Solenoid:

$B=\mu_0 n I$

9. Force Between Two Parallel Current-Carrying Conductors:

$\frac{F}{l}=\frac{\mu_0 I_1 I_2}{2 \pi r}$

10. Torque on a Current Loop:

• Torque on a current loop

$
\tau=N I A B \sin \theta
$

• Magnetic dipole moment

$
\vec{m}=N I \vec{A}
$

11. Potential Energy of Magnetic Dipole:

$U=-\vec{m} \cdot \vec{B}$

12. Moving Coil Galvanometer:

• Current sensitivity

  $
  \frac{\theta}{I}=\frac{N B A}{k}
  $

• Voltage sensitivity

$
\frac{\theta}{V}=\frac{N B A}{kR}
$

11. Conversion of Galvanometer:

• Shunt resistance for ammeter

$
S=\frac{G I_g}{I-I_g}
$

• Series resistance for the voltmeter

$
R=\frac{V}{I_g}-G
$

Moving Charges and Magnetism: Previous Year Questions

Moving Charges and Magnetism Previous Year Questions will assist the students to learn about the exam pattern and to study the most popular concepts of magnetism to be tested. The general questions are based on the magnetic force, the motion of charged particles, the Biot-Savart law, the Ampere circuital law, the torque on a current loop, and measuring devices. The use of PYQs enhances conceptualization, accuracy in numbers, and time efficiency. The repetitive practice of the past year's questions has been greatly successful in achieving a good score in Class 12 board tests, JEE Main, and NEET.

Question 1:

A long solenoid of 50 cm length having 100 turns carries a current of 2.5 A. The magnetic field at the centre of the solenoid is: $ \left(\mu_o=4 \pi \times 10^{-7} T m A^{-1}\right)$

Solution:

Magnetic field at centre of solenoid $=\mu_0 n I$

$
\begin{aligned}
& n=\frac{N}{L} \\
& =\frac{100}{50 \times 10^{-2}} \\
& =200 \mathrm{tums} / \mathrm{m} \\
& I=2.5 \mathrm{~A}
\end{aligned}
$
On putting the values,

$
\begin{aligned}
& B=4 \pi \times 10^{-7} \times 200 \times 2.5 \\
& =6.28 \times 10^{-4} T
\end{aligned}
$

Question 2:

Two similar coils are kept mutually perpendicular such that their centres coincide. At the centre, find the ratio of the magnetic field due to one coil and the resultant magnetic field through both coils if the same current is flown :

Solution:

Suppose the magnetic field produced by each coil is $B$.
The two coils are kept perpendicular; hence, the angle between them is $90^{\circ}$. Therefore, the resultant magnetic field is given by

$
\begin{aligned}
& =\sqrt{B^2+B^2+2 B \cdot B \cdot \cos 90^{\circ}} \\
& =\sqrt{2 B^2+2 B^2 \times 0} \\
& =\sqrt{2 B^2}=B \sqrt{2}
\end{aligned}
$
Hence, the ratio of the magnetic field due to one coil and the resultant magnetic field is given by

$
=\frac{B}{\sqrt{2 B}}=1: \sqrt{2}
$

Question 3:

$A$ and $B$ are two concentric circular conductors of centre 0 and carrying currents $I_1$ and $I_2$ as shown in the figure. The ratio of their radii is $1: 2$ and the ratio of the flux densities at 0 due to $A$ and $B$ is $1: 3$. The value of $I_1 / I_2$ will be:

Solution:

Magnetic field produced at the centre by loops

$
\begin{aligned}
& B_1=\frac{\mu_0 I_1}{2 r_1}, s \quad B l 2=\frac{\mu_0 I_2}{2 r_2} \\
& \frac{B_1}{B_2}=\frac{I_1}{I_2} \times \frac{r_2}{r_1}
\end{aligned}
$
But given $\frac{B_1}{B_2}=\frac{1}{3}$

$
\begin{aligned}
& \therefore \frac{1}{3}=\frac{I_1}{I_2} \times \frac{2}{1} \\
& \therefore \frac{I_1}{I_2}=\frac{1}{6}
\end{aligned}
$

Moving Charges and Magnetism in Different Exams

The chapter Moving Charges and Magnetism in Physics, Class 12, is a high-weightage chapter which is important to understand the magnetic effect of the electric current and of the moving charges. Questions in this chapter are conceptual and involve numerical problem-solving. The awareness of exam-wise focus areas and weightage would enable the students to prepare better and efficiently for board and competitive exams.

Important Books and Resources for Moving Charges and Magnetism

In order to develop good conceptual clarity and problem-solving skills in Moving Charges and Magnetism, the students need to consult a combination of textbooks, reference guides, and problem-solving books. These materials assist in clarification of important concepts, solving solved problems, and they give sufficient practice before board examinations as well as competitive exams such as JEE Main, JEE Advanced and NEET.

NCERT Resources for Moving Charges and Magnetism

The materials on Moving Charges and Magnetism presented by NCERT offer conceptual explanations which are in full compliance with the Class 12 Physics syllabus. The NCERT textbook and example problems are useful in making the students comprehend the magnetic effects of current, the motion of charged particles and measuring tools systematically. Such resources will be very useful to develop good basics and train successfully in board exams and competitive exams like JEE Main and NEET.

• NCERT solutions for class 12 physics chapter moving charges and magnetism
• NCERT exemplar solutions for class 12 physics chapter moving charges and magnetism
• NCERT notes for class 12 physics chapter moving charges and magnetism

NCERT Subjectwise Resources

NCERT subject-wise materials are organised and syllabus-based learning content on various subjects, which assist students in developing a good conceptual basis. They consist of textbooks, exemplar problems, and solutions and can thus be very helpful in the preparation for the board exams and even competitive exams such as JEE and NEET.

Practice Questions Based on Moving Charges and Magnetism

Moving Charges and Magnetism Practice Questions are needed to reinforce the knowledge of the magnetic effects of moving charges and electric currents. These questions touch upon such important concepts as magnetic force, motion of charged particles, Biot-Savart law, Ampere circuital law, torque on a current loop, and measuring instruments. Regular practice improves numerical accuracy, conceptual clarity, and problem-solving speed. The diversity of the problems enables an effective preparation of students towards the Class 12 board-exam and other competitive exams such as JEE Main and NEET.

Conclusion

The chapter Moving Charges and Magnetism lays a solid groundwork of knowledge regarding the magnetic effects of the moving electric charges and conductors carrying current. Through continuous drilling on the basic concepts, major formulas, and problem-solving methods of magnetic force, moving charged particles, magnetic fields, and electromagnetic laws, the students can gain clear conceptual knowledge. This special training boosts confidence and is very useful not only for passing board exams but also in passing competitive exams like JEE Main, JEE Advanced and NEET.