Magnetic Field An area of influence around a moving charge which produces magnetic field lines (like Electric Field Lines). Only ferromagnetic materials produce magnetic effects or magnetism (ie The Earth) Magnetic fields are vectors represented by the symbol “B” Electric Currents produce magnetism Right Hand Rule 1 i.e. doorbells (solenoids and electromagnets)

F=BIL If a wire is placed into a magnetic field, the wire experiences a force. The Force on the wire is dependent on the current in the wire, the length of the wire and the strength of the magnetic field.

TERMS and UNITS Electromagnetism- current through wire that produces a magnetic field X- field going into paper O- field going out of paper B- magnetic field (Tesla) F- force (Newton) I- current (Ampere)

Example A 10.0 m long high-tension power line carries a current of 20.0 A perpendicular to the Earth’s magnetic field. The power line experiences 0.011 N of force. What is Earth’s magnetic field?

F = Bvq The size of a magnetic field is related to the amount of magnetic force experienced by a moving charge somewhere in the field. If you put a charged particle in a magnetic field, it will experience a force and it will move. The velocity of the charge is directly proportional to the Force on the charge.

Example Dean is hunting in Texas at a location where Earth’s magnetic field is 7.0 x 10-5 T. He shoots by mistake a duck decoy, and the rubber bullet he is using acquires a charge of 2.0 x 10-12 C as it leaves the gun at 300 m/s, perpendicular to the Earth’s magnetic field. What is the magnitude of the magnetic force acting on the bullet?

Example Kron, the alien freedom fighter from planet Krimbar, shoots his gun that fires protons at a speed of 3.0 x 106 m/s. What is Krimbar’s magnetic field if it creates a force of 2.88 x 10-15 N on the protons?

Electromagnetic Induction the relative motion between the wire and the magnetic field that produces current in a circuit. Electromotive Force (EMF)- potential difference (Voltage) Equation: EMF = B x L x v

Example An EMF of 0.12 V is induced in a copper wire 30 cm long that is perpendicular to a field of 0.80 T and moves at right angles to the field. At what speed is the wire moving?

Transformer Power In = Power Out VpIp = VsIs In order for power companies to save energy and cost, they will send power out in the form of more current and less voltage.

Example A cell phone charger is plugged into a 110V outlet at your home and draws .1A while supplying 2A to your phone. What is the voltage present in your cell phone? Think about your answer, did this process increase voltage or decrease?

Ns=Vs Np Vp A transformer is a device that produces a change in voltage in an alternating current. A transformer consists of a piece of iron with wire wrapped around both sides.

Transformer

Example A hydroelectric plant in Niagra Falls sends 3000 V to a transformer in a substation that steps it up to 120,000 V for transmission to homes in New York City. If the primary coil contains 2000 turns, how many turns are there in the secondary coil of the substation transformer? Is this a step up transformer?

A Generator converts mechanical energy into electrical energy. Maximum Current when perpendicular No current if parallel S N O X

Electric Motor Electric Motors convert electrical energy into mechanical energy.

WHAT ARE SOME USES FOR MAGNETS? Motors, Generators, Compasses, Speakers and much, much more!

Forces caused by Magnetic Fields Third Right Hand rule – used to determine the direction of force when the current and magnetic field are known. The magnitude of force in a magnetic field. Equation: Force = strength x current x length F= B x I x L Magnetic Induction- strength of magnetic field. Units: Tesla ( newton-amp/meter)

Forces cont’d Galvanometer- device used to measure very small current Force on a current-carrying wire in a magnetic field causes an electric motor to rotate. Magnetic fields change the direction of electrons in a television picture tube.

Electromagnetic Induction the relative motion between the wire and the magnetic field that produces current in a circuit. Electromotive Force (EMF)- potential difference (Voltage) Equation: EMF = B x L x v

Lenz’s Law The direction of the induced current is such that the magnetic field resulting from the induced current opposes the change in flux that caused the current. Faraday’s Law- The induced voltage in a coil is proportional to the product of the number of loops and the rate at which the magnetic field changes within those loops.

Generators and AC Generator- movement of a coil in an electromagnet to produce electrical energy from mechanical energy. Alternating Current- current that changes magnitude and direction periodically.