NCERT Class 12 Physics Chapter 4 Notes Moving Charges and Magnetism - Download PDF

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• NCERT Notes Class 12 Physics
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• NCERT Exemplar Class 12 Physics Chapter 4 Solutions Moving Charges And Magnetism

Force Applied To A Moving Charge:

A moving charge is the source of the magnetic field.

Assume q is a positive charge moving in a uniform magnetic field Band velocity v

[ k is constant]

Where in S.I. system k=1

F=qvBsinθ and

Magnetic field strength B:

In the equation, we can observe this F=qvBsinθ, if

i.e.,

then F=B

As a result, magnetic field strength can be defined as the force experienced by a unit charge moving at unit velocity perpendicular to the magnetic field's direction.

Some cases for this:

1. If θ=0^o or 180^o

There will be no force acting on a charged particle moving parallel to the magnetic field.

2. When

A charged particle in a magnetic field will not experience any force when it is at rest.

3. When then the force will be maximum

The highest force will be experienced by a charged particle moving perpendicular to the magnetic field.

• S.I. unit of magnetic field intensity:

The S.I unit is tesla (T).

When

That is

Then B=1T

When a charge of 1C at a velocity of 1 m/s encounters a force of 1N while moving at a right angle to a magnetic field, the strength of the magnetic field is called 1T.

• Biot-Savart’s Law:

Because of the current element dl, the strength of magnetic flux density or magnetic field at a point P (dB) will be dependent on

After we combine them:

Where

,

dB will be perpendicular to the plane containing dl

• Biot-law Savart's applications:

A magnetic field (B) is maintained at the centre of a circular current-carrying coil with a radius of r.

The magnetic field in the centre of a circular coil with n turns will be, if there are n turns.

The number of turns of the coil is denoted by n. I will be the coil's current, and r will be the radius of the coil.

Magnetic field caused by a straight conductor carrying current:

The perpendicular distance of the conductor from the place where the field is to the measured value will be denoted by a.

Φ₁ and Φ₂ will be the angles formed by the conductor's two ends meeting at the location.

A semi-circular current-carrying conductor will have a magnetic field at its centre.

The magnetic field at the centre of a circular current-carrying conductor arc with an angle of θ at the centre will be,

Ampere Circuital Law:

In a vacuum, the magnetic field line integral around any closed passage is mu zero times the entire current via the closed path. that is

• 7. Application of Ampere’s circuital law:

• Magnetic field caused by a current-carrying solenoid,

• Magnetic field caused by a toroid or endless solenoid,

• Charged Particle Motion in a Uniform Electric Field: –

The path of a charged particle in an electric field is called a parabola.

Equation of the parabola be

Where x is the electric field's width.

y is the particle's deviation from its straight path.

v is the charged particle's speed. q is the particle's charge.

E denotes the strength of the electric field. Let m be the particle's mass.

In a uniform magnetic field B, the path of a charged particle moving at producing an angle with B will be a helix. Because the charged particle will not be supplied a force by the component of velocity , the particle will move forward with a fixed velocity in the direction of B. The other component, , will produce the force , which will provide the necessary centripetal force to the charged particle moving along a circular route with radius r.

Centripetal force =

Angular velocity of rotation =

Frequency of rotation =

The time period of revolution =

• Cyclotron:

This is a technology that we use to accelerate positively charged particles and thereby energize them. This can be achieved by immersing the particle in a perpendicular magnetic field that oscillates and an electric field that oscillates. A circular path will be followed by the particle.

Centripetal force=magnetic Lorentz force

the radius of the circular path

Time for travelling a semicircular path =

=constant When is the particle's highest velocity and is the maximum radius of its path, we can say that

The maximum kinetic energy of the particle =

=

The time period of the oscillating electric field =

Cyclotron frequency =

Cyclotron angular frequency =

• Force acting on a current-carrying conductor kept in a magnetic field will be

I be the current flowing through the conductor in this case.

B be the strength of the magnetic field.

l denotes the conductor's length.

be the angle formed by the current direction and the magnetic field.

If

There will be no force acting on a conductor if it is kept parallel to the magnetic field.

If

F will be maximum

The conductor will be experiencing maximal force if it is kept normal to the magnetic field.

• The force between two parallel current-carrying conductors: –

1. If the current flows in the same direction, the two conductors will be drawn together by a force.

2. When the current is flowing in the opposite direction, the two conductors repel each other with equal force.

• Torque Experienced on a Current-Carrying Coil Kept in a Magnetic Field:

where M be the magnetic dipole moment of the coil

Where n is the coil's number of turns.

I represent the current flowing through the coil.

B is the magnetic field's intensity.

The coil's area is denoted by the letter A.

The angle between the magnetic field B and the coil's normal to the plane will be α

• Moving Coil Galvanometer:

This is based on the premise that if a coil carrying electricity is held in a magnetic field, it will experience torque. Because of the phosphor bronze strip, there is a restoring torque, which returns the coil to its usual position.

In equilibrium,

Deflecting torque = Restoring torque

where Galvanometer constant

The deflection made if the unit current is passed through the galvanometer is the current sensitivity of the galvanometer.

The deflection caused by a unit potential difference placed across the galvanometer is known as voltage sensitivity.

• The maximum sensitivity of the galvanometer is having some conditions: -

If a modest current causes a big deflection, the galvanometer is said to be sensitive.

• Galvanometer To Voltmeter And Ammeter Conversion:

1. By connecting a high resistance to a galvanometer, it can be turned to a voltmeter.

Total resistance of voltmeter = Rg + R

Where Rg be the galvanometer resistance.

R be the resistance added in series.

Current through the galvanometer =

Here V is the potential difference across the voltmeter.

By connecting a low resistance in parallel with a galvanometer, it can be transformed into an ammeter (shunt)
Shunt =

where Rg be the galvanometer’s resistance.

The effective resistance of the ammeter will be,

Significance of NCERT Class 12 Physics Chapter 4 Notes

Comprehensive Revision: These Moving Charges and Magnetism class 12 notes provide a concise summary of Chapter 4 from the NCERT Class 12 Physics textbook, allowing students to revise key concepts before exams.

Understanding Core Concepts: Class 12 physics chapter 4 notes help students understand important topics in moving charges and magnetism, such as magnetic fields, the magnetic force on a current-carrying conductor, and the Biot-Savart law.

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Overall, these Physics class 12 chapter 4 notes pdf help students learn, revise, and prepare for exams by ensuring a solid understanding of moving charges and magnetism concepts.

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