Forcing a wire through a magnetic field produces (generates) a current in the wireExample: GeneratorConverts mechanical energy into electrical

energy

Generators spin a bundle of wire attached to a motor through magnets causing current or electricity to be produced

Electromagnetic induction- a current is produced in a wire by passing a magnet near itThe magnetic field lines (flux) crossing the

wire cause the electrons in the wire to move (electricity)

Force is greatest when the charge moves perpendicular to the magnetic field

At other angles the force is less The force is 0 when the charge moves

parallel to the magnetic field

Magnetic Flux ( Φ ) - The # of magnetic field lines passing through a given area

Magnetic Flux( Φ ) =BA

Where is the greatest concentration of magnetic flux lines?Near the poles (ends)

A current carrying wire placed in a magnetic field experiences a force

Example: MotorsConverts electrical energy into mechanical

energy

1. Keep hand flat 2. Thumb in the direction of the current 3. Fingers in the direction of the

magnetic field 4. Palm in direction of the force

All are perpendicular to each other

3 factors affect the magnitude of the force on a current-carrying wire placed in a magnetic field

1. Strength of the magnetic field 2. Amount of current (velocity) 3. Length of the wire

F=B I l

F=Force (N) B=magnetic field strength (N/am) I=Current in wire (a) l=Length of the wire perpendicular to

the field (m)

A segment of wire .040 m long is perpendicular to the magnetic field inside a solenoid. When a current of 3.0 amps flows through the wire, it takes a force of 0.020 Newtons to balance the wire. What is the magnetic field inside the solenoid. F= B I L

.020N = B (3.0 amps) (.040m)

B = .17 N / amp m

The formula can also be written for any single charge moving through a magnetic field

F=Bqv

F=Force (N) B=Magnetic field strength (N/am) q=charge (C) v=velocity of charge (m/s)

When not just any charge, but an electron

F=Bev

e=charge for an electron (1.6 X 10^-19 C)

An electron moves through a magnetic field of .20 N/Am at a speed of 300,000 m/s. What is the force on the charge due to this field?

F = B e vF = .20 N/Am (1.6 x 10-19 C)(300,000 m/s)

F = 9.6 x 10-15 N

Voltage-Energy needed to move a charge

Helps explain how motors work Motors convert electrical energy into

mechanical energy

Faraday’s Law- Voltage (current) induced in a wire is proportional to the rate of magnetic flux cutting across the wire

What happens when you increase voltage? Increase magnetic flux (the # of magnetic

field lines/area)

Relative Motion-The movement of one object with respect to another object

Lenz’s Law-The current induced in a wire is in such a direction that its magnetic field opposes the changing field that induced it

Emf = -B l v

Emf=electromotive force (volts) B=Magnetic Field Strength l=length of wire v=velocity

A wire of length 50 cm is moving at a speed of 2.0 m/s perpendicular to a magnetic field of 0.75 N/A m. What emf is induced in the wire?

Emf = -B l v

Emf = - (.75 N/A m) (.50 m) (2.0 m/s)

Emf = 0.75 Volts

Transformers- A device to increase or decrease voltage

http://phet.colorado.edu/en/simulation/faraday

N1/N2 = V1/V2

N=number of turns of wire V=voltage (volts)

If the primary coil having 5 turns of wire contains 20 volts, what is the voltage in the secondary coil having 10 turns?

N1/N2 = V1/V2

5 / 10 = 20 / V2

V2 = 40 Volts

1. A segment of wire 25 cm long is in a magnetic field of .75 N/A m. The force on the wire is 0.30 N. What is the current flowing through the wire?

2. A charge (2.3 X 10^-15 C) moves through a magnetic field at 225,000 m/s. What is the magnetic field strength if the force is 4X10^-4 N?