11TH GRADE · MAGNETISM

Magnetic field and forces

Induction, Ampere force, Lorentz force and charge motion.

28 minutes21 theory cards

LESSON MATERIAL

Basic Concepts

Magnetic field

A field created by moving charges and acting on moving charges and currents.

The magnetic part of the force is perpendicular to the speed of the charge, therefore it changes the direction of movement, but does not do work.

Ampere power

The force of a magnetic field on a conductor carrying an electric current.

The force is maximum when the conductor is perpendicular to the field and is zero when the current is directed along the magnetic induction.

Lorentz force

The force of electric and magnetic fields on a moving charge.

The electrical part of the force can change the speed modulo, while the magnetic part is directed across the movement and bends the trajectory.

LESSON MATERIAL

Physical quantities

Magnetic induction

B

Strength characteristics of the magnetic field.

Unit: Tesla · $\mathrm{Tl}$

Ampere power

F_A

The magnetic field force acting on a current-carrying conductor.

Unit: newton · $\mathrm{N}$

Active conductor length

l

The length of a section of conductor located in a magnetic field.

Unit: meter · $\mathrm{m}$

Angle to magnetic field

\alpha

The angle between the direction of current or speed and the vector of magnetic induction.

Unit: radian · $\mathrm{rad}$

Magnetic Lorentz force

F_L

The force of a magnetic field acting on a moving charge.

Unit: newton · $\mathrm{N}$

Charge speed

v

The speed of movement of a charged particle.

Unit: meter per second · $\frac{\mathrm{m}}{\mathrm{s}}$

Particle charge

q

Electric charge of a moving particle.

Unit: pendant · $\mathrm{Kl}$

Particle mass

m

Inert mass of a moving particle.

Unit: kilogram · $\mathrm{kg}$

Trajectory radius

R

The radius of the circle along which the charge moves.

Unit: meter · $\mathrm{m}$

Maximum torque

M_{\max}

The greatest torque acting on the current-carrying frame.

Unit: newton meter · $\mathrm{N}\cdot\mathrm{m}$

Frame area

S

Area of the current loop.

Unit: square meter · $\mathrm{m}^2$

LESSON MATERIAL

Lesson formulas

Determination of magnetic induction

B=\frac{F_A}{Il}=\frac{M_{\max}}{IS}

Magnetic induction can be determined by the force on the conductor or the maximum moment on the frame.

Definition of Tesla

1\,\mathrm{Tl}=1\,\frac{\mathrm{N}}{\mathrm{A}\cdot\mathrm{m}}

One tesla creates a force of one newton on a one meter long conductor with a current of one ampere.

Ampere power

F_A=IlB\sin\alpha

The Ampere's strength depends on the current, the length of the conductor, the induction and the angle.

Magnetic Lorentz force

F_L=qvB\sin\alpha

The magnetic force on a charge depends on the charge, speed, induction and angle.

Charge movement in a circle

qvB=\frac{mv^2}{R}

Magnetic force plays the role of centripetal force.

Condition: The speed is perpendicular to the magnetic induction.

Charge trajectory radius

R=\frac{mv}{qB}

The radius increases with mass and speed, decreases with charge and induction.

Charge reversal period

T=\frac{2\pi R}{v}=\frac{2\pi m}{qB}

The period of revolution in a uniform field does not depend on the speed.

Related formulas

Magnetic inductionB · Tl Speedv · m/s

PRACTICE

Tasks on the topic

Magnetism11 class · 11 problems