Chapter 22 Magnetism and its Uses
Objects 22.1 Describe the properties of magnets 22.1 Define the region of force around a magnets 22.1 Model magnetic behavior using domains
Objects 22.2 Explain the magnetic effects of a current in a wire 22.2 Compare and contrast ammeters and voltmeters 22.2 Describe the function of an electric motor.
Objects 22.3 Describe how a generator produces an electric current using electromagnetic induction 22.3 Distinguish between alternating and direct current 22.3 Explain how a transformer can step up or step down the voltage of an alternate current
Objectives 22.4 Describe the characteristics of superconductors 22.4 Consider various applications of superconductivity
Key Words Magnetism Magnetic Pole Magnetic Field Magnetic Domain Electromagnet Ammeter Voltmeter Electric Motor Electromagnetic Induction Generator Direct Current Alternating current Transformer Solenoid
Magnetism Magnetism is a property of matter in which there is a force of attraction or repulsion between unlike or like poles One positive end, one negative end Most metals area actually NOT magnetic Iron, Cobalt and Nickel metals which are actually magnetic Other metals can be temporary magnets
Opposites Attract
The Earth Earth is a big magnet. The actual location of the magnetic poles change every year by about 40 miles Earth’s magnetic poles change yearly
Magnetic Declination Your compass points to the magnetic pole, not to the true north pole As you approach the poles, you have to add/subtract degrees to go the right direction Compass is wrong close to poles
The north arrow on the compass rose (the large N) is pointed towards the place on the horizon directly beneath the North Star! That is, towards true north! And the needle (of course) points towards magnetic north! So the magnetic declination for this locality is 45 degrees west
Magnetic Domains Groups of atoms with aligned magnetic poles are called
Magnetic Fields Points towards the South Pole So, South must be Negative end Since magnetic fields point towards the negative charge Magnetic Pole: End of magnet, strongest magnetic field Earth’s North pole Is the south magnet
Electromagnet A type of magnet created by current passing through a coil Electromagnetic Induction: The process by which moving a wire through a magnetic field produces a current
Solenoid: Coils wrapped around with a current moving through Solenoid: Coils wrapped around with a current moving through. Used in MRI’s
Thumb points towards the North End
Magnetic Field Force The current causes the magnetic field The magnetic field in turns pushes on the wire Electric Motor: Turns electrical energy into mechanical energy
Reading Current and Voltage Voltmeter: Determines the voltage drop across a resistor Ammeters: Determine the current through a wire Determined by deflection caused by the magnetic field
Generator Produces electric current by rotating wires in a magnetic field See simulator
Direct Current DC = Direct Current. The flow (current) of electrons is in one direction Like a river runs only down hill, direct current only flows one way. Batteries provide this type of current
Alternating Current AC = Alternating Current Electrons flow back and forth. The electrons are pushed one way, then pushed the other way. The electrons stay in roughly the same area, just going back and forth. Our outlets provide this, alternating current.
Alternating Current In the USA, there are three wires that transmit the flow of energy. Two are at + or – 120 Volts (180 degrees out of phase) One is at 0 Volts The US has adopted a frequency of 60 Hz The polarity (direction of electrons) changes 120 times per second Actual voltage of peaks are + and – 170 volts
Transformers Step Up or Step Down the Voltage A transformer is just a piece of iron with a pair of wires coiled around it - one with many more turns in the coil than the other. The coils of wire are not physically connected. The iron core is immersed in an insulating oil bath which does not conduct electricity well. Step Up or Step Down the Voltage
Transformers