# Magnetic fields Flashcards

What is Maxwell’s corkscrew rule / right hand rule?

This shows the direction of the magnetic field around a current carrying wire.

> Thumb - Direction of current

> Fingers - Direction of magnetic field

What is the symbols used for the magnetic field moving in and out of the plane of the paper?

> Out of the paper: ⊙

> In to the paper: ⊗

What is Flemmings left hand rule?

This shows the force applied to a current carrying wire placed into a magnetic field:

> Thumb - Force / Motion

> First finger - Magnetic field

> Second finger - Current

What is the equation that comes from Flemmings left hand rule?

F = BILsinθ

How can the equation F = BILsinθ be combined with current density and simplify it?

F = BAneVdLsinθ N = nAL (Number of electrons) q = Ne F = BqVdsinθ

What is the hall effect?

> When current flows through a wire in a perpendicular magnetic field

Electrons experience a force perpendicular to their motion

This causes electrons to accumulate onto one face of a material giving it a negative charge

This produces an electric field within the wire which balances the magnetic field

The hall voltage can be measured across the two faces of the wire

How is the hall voltage used?

It is used to calculate the carrier density:

> E = - dV/dx - This can be measured

> F = BqVd => Eq = BqVd => E = BVd

> E = BVd - The magnetic field is known so Vd is calculated

> I/A = neVd => I/AeVd = n

- The Current and crossectional area can be measured

- The electron charge is known

- The Vd is calculated so the number density can be calculated

What is Lenz’s law?

‘The induced current flows always in such a direction as to oppose the change causing it’

What is the Magnetic flux density?

The magnetic flux per unit of area

> Symbol: B

> Units: Tesla

What is magnetic flux?

The quantity of magnetic flux from a magnetic / electromagnet

> Symbol: ϕ

What is the equation to calculate the magnetic flux?

ϕ = BAcosθ or ϕ = NBAcosθ θ = the angle between the direction of the magnetic field and the perpendicular to the face of the area

What is induced EMF?

This is the voltage induced into a wire when it is moved through a magnetic field.

> Symbol: V

What is the equation to calculate induced EMF?

V = - dθ/dt

Why is there a negative in the equation used to calculate induced EMF?

Because of Lens’z law

THIS IS IMPORTANT

What affects the magnitude of induced EMF?

> The size of the area

The size of the magnetic field

The faster spinning of the coil (The greater the rate of change of magnetic flux, the greater the induced EMF)

The number of turns of the coil

What is the equation for the induced EMF for a dynamo and what is its rearrangement?

> V = - dNBAcosθ/dt V = -NBA d/dt(cosθ) V = -NBA × -sin(θ)dθ/dt V = NBAsinθ×dθ/dt > V = NBAωsinθ > ω = 2π/t (angular frequency