Electromagnetic Induction

The interaction between current and magnetic field

Remember from Year 12

• When current flows through a wire a magnetic field is created around the wire

• And if the wire is coiled (to form a solenoid)

The relationship between electricity and magnetism (Motor effect)

Just like;

Magnetic Fields

Remember from Year 12

• When a wire moves through a magnetic field a voltage is induced

• Or a magnetic field moves through a coil a voltage is induced

The relationship between magnetism and electricity (Generator effect)

Using Your Hand and Formulae

)θ(sinBILF

BvLV

)θ(sinBqvF

• Right-hand grip rules• Right –hand slap rule

• Force on a current carrying wire (motor effect)

• Induced voltage (generator effect)

• Force on a charge

The Motor Effect

• A current carrying wire at an angle to a magnetic field experiences a force

• This is as a result of the interaction between the magnetic field and the magnetic field around the wire.

Electric Motors

• Most electric motors use electricity to make magnetism

-the motor effectThe use of electric motors is widespread with most of us using many each day

RH Grip Rule -Wire

RH Grip Rule -Solenoid

RH Grip Rule -SolenoidPredict the direction of the North

magnetic pole

RH Grip Rule -SolenoidPredict the direction of the North

magnetic pole

RH Grip Rule -SolenoidPredict the direction of the North

magnetic pole

RH Grip Rule -SolenoidPredict the direction of the North

magnetic pole

RH Motor Rule Examples

I

I

Predict the direction of the force on the wire and label the positive end of

the wire

RH Motor Rule ExamplesI

I

Predict the direction of the force on the wire and label the positive end of

the wire

RH Motor Rule Examples

I

I

Predict the direction of the force on the wire and label the positive end of

the wire

RH Motor Rule ExamplesPredict the direction of the force on

the wire and label the positive end of the wire

RH Motor Rule ExamplesPredict the direction of the forces

on the wire coil at 1 and 2

Force on a Charge

• A single charge or a charged object will also experience a force as it moves through a magnetic field as it too creates a magnetic field as it moves (just like current in a wire)

Force on a Charge

Slap Rule for Force on a Charge

v

v

Force on a Charge

http://www.stmary.ws/highschool/physics/home/animations3/magnetism/charge_mag_field.swf

Force on a ChargePredict the direction of the force on

the moving positive charge

+q

Force on a ChargePredict the direction of the force on

the moving positive charge

+

Force on a ChargePredict the direction of the force on

the moving negative charge

-q

Force on a ChargePredict the direction of the force on

the moving negative charge

-

Force on a Charge –the maths

• Force on moving charges in a wire;

• Force on moving charges on their own;

)θ(sinBILF

)(sinBqvF Where;

F=force (N)B= magnetic field strength

(T)q=charge on the object (C)v=velocity of the charge

(ms-1)=angle from field lines ()

Exercises

1. Find the force on an electron (1.60×10-19C) travelling at 3×107 ms-1 perpendicular to a magnetic field of 0.18T

9×10-13N2. Calculate the charge of a particle travelling

at 340ms-1 perpendicular to a 1.2T magnetic field that experiences a force of 3.5×10-12N

8.6×10-15C

Electricity Generation

• Most generators use magnetism to generate electricity

-The generator effect

Induction -the Generator Effect

• A wire that moves through a magnetic field has a voltage induced across it and therefore a current is induced

• Of course the magnetic field can move past the wire and cause induction also

• Induction is the result of the interaction between the magnetic field and the negatively charged electrons in the wire

RH Generator Rule

•To predict the direction of the induced current use the modified RH slap rule•As with the RH slap rule for the motor effect, the thumb is the cause (the velocity of the wire for a generator), the fingers are the field lines, and the “slap” is the direction of the resultant (in this case the current)

v

B

I

RH Generator Rule Examples

v

Predict the direction of the current and label the +ve end of the wire

RH Generator Rule Examples

v

v

Predict the direction of the current and label the +ve end of the wire

vv

RH Generator Rule ExamplesPredict the direction of the current and label the +ve end of the wire