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11TH GRADE · MAGNETISM

Magnetic flux and induction

Flux, electromagnetic induction, self-induction and field energy.

30 minutes18 theory cards
Open interactive lesson

LESSON MATERIAL

Basic Concepts

2

Electromagnetic induction

The occurrence of EMF in a circuit when the magnetic flux through it changes.

EMF is created precisely by a change in magnetic flux; the resulting current, according to Lenz's rule, counteracts this change.

Self-induction

The occurrence of EMF in a circuit when its own current and magnetic flux change.

The coil prevents a rapid change in its own current: the greater the inductance and the rate of change of current, the greater the EMF.

LESSON MATERIAL

Physical quantities

8

Magnetic flux

Φ\Phi

A measure of the magnetic field passing through a surface.

Unit: weber · Vb\mathrm{Vb}

induced emf

Ei\mathcal{E}_i

EMF that occurs when magnetic flux changes.

Unit: volt · V\mathrm{V}

Number of turns

nn

The number of turns of conductor in a coil.

Unit: dimensionless quantity

Magnetic flux change

ΔΦ\Delta\Phi

The difference between the final and initial magnetic fluxes.

Unit: weber · Vb\mathrm{Vb}

Inductance

LL

The ability of a circuit to create its own magnetic flux when current passes.

Unit: Henry · Gn\mathrm{Gn}

Current change

ΔI\Delta I

The difference between the final and initial currents.

Unit: ampere · A\mathrm{A}

Self-induced emf

Esi\mathcal{E}_{\text{si}}

EMF arising due to changes in current in the circuit itself.

Unit: volt · V\mathrm{V}

Magnetic field energy

WW

The energy stored in the magnetic field of the coil.

Unit: joule · Dzh\mathrm{Dzh}

LESSON MATERIAL

Lesson formulas

8

Magnetic flux

Φ=BScos⁡α\Phi=BS\cos\alpha

Magnetic flux depends on the induction, area and orientation of the surface.

Weber's definition

1 Vb=1 V⋅s=1 Tl⋅m21\,\mathrm{Vb}=1\,\mathrm{V}\cdot\mathrm{s}=1\,\mathrm{Tl}\cdot\mathrm{m}^2

One weber is equal to a volt-second and a tesla-square meter.

Law of Electromagnetic Induction

Ei=n∣ΔΦ∣Δt\mathcal{E}_i=n\frac{\lvert\Delta\Phi\rvert}{\Delta t}

The module of the induced emf is equal to the rate of change of the total magnetic flux.

Self-induced emf

Esi=L∣ΔI∣Δt\mathcal{E}_{\text{si}}=L\frac{\lvert\Delta I\rvert}{\Delta t}

The self-inductive emf is proportional to the inductance and the rate of change of current.

Coil magnetic field energy

W=LI22W=\frac{LI^2}{2}

The energy of the magnetic field depends on the inductance and the square of the current.

EMF of conductor movement

E=Blvsin⁡α\mathcal{E}=Blv\sin\alpha

EMF occurs when a conductor moves in a magnetic field.

Maximum EMF of the rotating frame

Emax⁡=nBSω\mathcal{E}_{\max}=nBS\omega

The amplitude of the EMF of the frame is proportional to the number of turns, induction, area and angular velocity.

Flux linkage and current

Φ=LI\Phi=LI

The self-magnetic flux is proportional to the inductance and current.

DIRECTORY

Related formulas

InductanceL · GnMagnetic fluxΦ · WbEnergyE, W · J

PRACTICE

Tasks on the topic

Magnetism11 class · 11 problems