# Chapter 4 – Moving Charges and Magnetism

The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:

Introduction

Do you ever wonder why a moving charge produces a magnetic field? Chapter 12 will discuss the explanation behind the same. Moving Charges and Magnetism will discuss topics of magnetic force, motion in a magnetic field, motion In combined electric and magnetic fields, and so on.

#### Magnetic Force

Magnetic force refers to the attraction or repulsion that arises due to the motion of electrically charged particles. Examples of magnetic force include action in electric motors and attractions between magnets and iron.

F= q[E(r)+v* B(r)] where,

F= Magnetic force

Q= Point of charge

Er= Electric filed

Br= Magnitude field

V= Velocity

A magnetic force depends on the following:

• The charge of the particle.
• The velocity of the particle.
• The magnetic field in which it is placed.

#### Motion In A Magnetic Field

In the motion of a charged particle in a magnetic field, the magnetic force is perpendicular to the velocity of the particle. Therefore no work is done, and no change in the magnitude of the velocity is produced.

#### Motion In Combined Electric And Magnetic Fields

When magnetic and electric fields are perpendicular to each other and are also perpendicular to the velocity of the particle, the electric and magnetic forces are in opposite directions.

Magnetic Field Due To A Current Element

According to the BIOT-SAVART LAW, the magnetic field dB due to the presence of an element dl which is carrying a continuous flow of current I at the point P at a distance r from the current element is to obtain a total field at P and integration of this vector expression over the entire length of the conductor.

Magnetic Field On The Axis Of A Circular Current Loop

The summation of elements dl over the loop yields 2πR, the circumference of the loop. Thus, the magnetic field at P due to the entire circular loop is:

#### Ampere's Circuital Law

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

#### The Solenoid And the Toroid

Let’s understand Solenoid in a manner where its length is larger than its radius. In a Helix form, a wire is wound keeping in mind that very little gaps are left in between any two turns. The wires are rendered from insulating each other as they are enameled. This is the reason each turn is taken as a closed circular loop.

To calculate the total magnetic field generated by the Solenoid vector, the sum of force generated by each turn is calculated. It can be noted that:

• The magnetic field formed inside a Solenoid is uniform in nature.
• It is also along the axis of the Solenoid.

A Toroid can be explained as a hollow circular ring on which a large number of turns of a wire are closely wound. It can also be imagined as a Solenoid which has been bent to close itself in a circular shape. It can be noted that:

• The magnetic field for a Toroid is zero inside and outside.
• The magnetic field inside a Toroid is constant in magnitude.
• The direction for the magnetic field is clockwise

#### Force Between Two Parallel Currents

We have seen electrostatic charges like charges that repel each other. However, in the case of parallel currents, it is observed that parallel currents attract each other and antiparallel currents repel each other. Therefore, it can be observed that:

• The parallel wires will repel each other if there is a current flowing in the opposite direction.
• The parallel wires will attract each other if there is a current flowing in the same direction.

#### The Moving Coil Galvanometer

Electric currents can be measured with an instrument known as a moving coil galvanometer. It is an instrument that can be used to measure currents as low as few microamperes due to its sensitive electromagnetic nature. There are two types of moving coil galvanometer, namely, Suspended coil galvanometer and Pivoted-coil or Weston galvanometer.

The moving coil galvanometer principle states that a current-carrying coil when placed in an external magnetic field experiences magnetic torque. The angle through which the coil is deflected due to the effect of the magnetic torque is proportional to the magnitude of current in the coil.

Having discussed the Magnetic Field On The Axis Of A Circular Current Loop, Ampere’s Circuital Law, The Solenoid And The Toroid, Force Between Two Parallel Currents, and The Moving Coil Galvanometer, etc., we hope to have solved your doubts and queries regarding the concepts of Moving Charges And Magnetism. For more detailed information on other topics covered in Physic CBSE class 12, keep visiting www.MSVgo.com

### High School Physics

• Alternating Current
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• Dual nature of Radiation and Matter
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### High School Math

• Algebra – Arithmatic Progressions
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### Middle School Science

• Acids, Bases And Salts
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### Middle School Math

• Area and Its Boundary
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• Time