Unit 8 – Electricity & Magnetism
Unit Big Idea: An electric current can produce a magnetic field, and a magnetic field can produce an
electric current.
Lesson 1 – Electric Charge and Static Electricity
Essential Question: What makes something electrically charged?
By the end of this lesson, you should be able to describe electric charges in objects and distinguish
between electrical conductors and insulators.
- electric charge – property that leads to electromagnetic interactions between the particles that make up
matter
- object can have positive (+) charge, negative (-) charge, or can be neutral with no charge
- review of the parts of an atom
- nucleus – dense center of an atom
- protons – positively charge particle found vibrating in the nucleus; charge of 1+
- neutron – neutral particle found vibrating in the nucleus; charge of 0
- electron – negatively charged particle moving around outside of the
nucleus; charge of 1- atoms usually have a no charge since the number of protons and
electrons are the same
- ion – atom that has lost or gained electrons and now has a charge
- electric force – force exerted by any two objects on each other
- do not need to touch to create electric force
- can either pull objects together or push objects apart
- strength of electric force depends on the charge of each objects and how close together they are
- like charges repel each other and opposite charges attract each other
- the greater the charge, the greater the electric force and the more the two particles will attract or
repel each other
- the distance between two objects affects the size of the electric force as well
- the closer together the charged objects are, the greater the electric force to attract or repel & the
farther apart they are the weaker the electric force to attract or repel
- objects become charged when their atoms gain or lose electrons through friction, contact,
or induction
- friction: happens when two objects rubbed together and transfer electrons between objects
- ex: rubbing balloon on hair moves electrons from hair to balloon; hair is positively
charged & balloon is negatively charged
- contact: when charged & uncharged object touch the charged object transfers part of its charge
to the uncharged object
- ex: person putting their hand on the Van de Graaff generator and charges their hair so it
stands up on end
- induction: way of rearranging the charges within an object without touching it
- ex: charging an aluminum pie plate by transferring the electrons from the plate to the
ground when grounding it and leaving the plate to have a positive charge
- static electricity – buildup of electric charge on an object
- extra positive or negative charge that builds up on an object unit it eventually moves elsewhere
- ex: clothes stuck together when pulled out of the dryer
- static electricity can build up in storm clouds with top of cloud positively charged & bottom of
cloud negatively charged; the ground becomes positively charged by induction
- electric discharge – when static electricity leaves the object
- lightening is example of electric discharge happening quickly
- electrical conductor – material that transfers an electric charge freely
- metal conduct electricity well (copper is used to make wires for electricity to flow through)
- electrical insulator – material that doesn’t transfer an electric charge easily
- electrons are tightly held together
- ex: plastic, glass, rubber, dry air
- plastic is used to coat wires to keep a person from being shocked by the electricity running
through the wire
- semiconductors – conduct electric charge better than an insulator but not as well as a conductor
- ex: silicon, germanium
- allow the control of the flow of an electric charge
- used in electronic devices
- conservation of charge – the total amount of charge stays the same because the electrons are moved
from one object to another – never created or destroyed
Lesson 2 - Electric Current
Essential Question: What flows through an electric wire?
By the end of this lesson, you should be able to describe how electric charges flow as electric current.
- electrical energy – energy of electric charges
- electric current - rate of flow of electric charges flowing through an area
- amount of charge that passes a location in a wire every second
- units: amperes or amps (A)
- a wire with a current of 2 A has twice as much charge passing by each second as a wire with a
current of 1 A.
2 types of electric current
- direct current (DC) – charges always flow in the same direction
- electric charges generated by batteries
- ex: flashlight, cars, cameras
- alternating current (AC) – charges repeatedly shift from flowing in one direction to flowing in the
reverse direction; current alternates direction
- ex: electrical outlet at home & most household appliances
- Two factors affect the current in a wire: voltage & resistance
- voltage - amount of work needed to move each unit of charge between two points.
- higher voltage makes a higher rate of flow of electric charges in a wire
- units are volts (V)
- sometimes called electric potential because it measures the electrical potential energy per unit
charge
- resistance – opposition to the flow of electric charge
- something that makes it harder for the electrical current to flow
- units are ohms (Ω, Greek letter omega)
- the higher the resistance, the lower the current
- What affects electrical resistance
- material’s composition or what it’s made of
- ex: copper and silver have low resistance and are very good electrical conductors
- ex: iron and nickel have higher resistance
- ex: plastics and other insulators have such a high resistance that electrical charges can’t
flow in them at all
- thickness of the wire
- the thicker the wire the less resistance & the thinner the wire the more resistance
- length of wire
- shorter wires have less resistance & longer wires have more resistance
- temperature
- cool wires have less resistance & warmer/hotter wires have more resistance
- Ohm’s Law:
Voltage = current x resistance
- V: Voltage
- measures the energy a power source gives to a circuit
- units are measured using Volts (V)
- I: Current
- measures the current of electrons in a circuit
- units are measured using amperes (amps)
- R: Resistance
- measures how hard / easy it is for electricity to flow through a material
- conductors have low resistance
- insulators have high resistance
- you can change how much resistance you have by changing the material, the thickness,
or the length of wire
- units are measured in ohms (Ω)
Lesson 3 – Electric Circuits
Essential Question: How do electric circuits work?
By the end of this lesson, you should be able to describe basic electric circuits and how to use electricity
safely.
- electric circuit – a complete closed path through which electric charges can flow
- all have 3 basic parts: energy source, electrical conductor, & load
- energy source converts some type of energy into electrical energy
- ex: batteries change chemical energy stored inside it into electrical energy;
solar cells in a solar panel change light energy from the sun into electrical energy:
power plants change chemical or nuclear energy into mechanical energy & electric generators in
the power plant change the mechanical energy into electrical energy
- power lines deliver all this electrical energy into houses, buildings, stores, etc
- electrical conductors are the materials that electric charges move easily through
- copper makes up most wires since it is a good conductor and costs very little money
- conducting wires connect all parts of an electric circuit
- copper wires are covered with an electrical insulator (like glass, plastic, or rubber) so the person
touching the wire won’t get shocked
- load is a device that uses electrical energy to work
- conductor connects load to the energy source
- ex: light bulbs, radios, computers, electric motors
- converts electrical energy into other forms of energy
- light bulb converts electrical energy into light and energy as heat
- doorbell converts electrical energy into sound waves
- cell phone converts electrical energy into electromagnetic waves that carry information
- electric circuits need an energy source, electrical conductor, & a load
- most electric circuits have many loads
- ex: circuit in your home may connect a lamp, TV, radio, VCR, game
station, & DVD player
- circuits can even connect devices in more than one room
- circuit diagram helps engineers and electricians design and install electric
circuits so they work correctly & safely
- diagram shows all the parts in the complete circuit and the
relationship among the different parts
- the symbols shown to the right are put together to show the
arrangement of parts in a circuit.
- a circuit diagram is like a road map for the moving electric charges
- the wire or any other conductor is a line
- electrical currents move continuously through a closed loop of an electrical
current
- opening the circuit stops the flow of electrical charges
- switch is a device that turns the electrical devices on & off
- switches are usually made from a piece of conducting material that can move
- when switch is open, the circuit is open; the circuit is not a closed loop so electricity doesn’t
flow
- when you turn a light switch on, the switch closes the circuit and charges flow through the light
bulb
- when you turn the light switch off, the switch opens the circuit and the charges stop flowing
- series circuit – all parts of the circuit are connected in a row that forms one path for the electric charges
to follow
- the current is the same for all of the loads
- all 3 light bulbs glow with the same brightness
- adding a 4th light bulb would lower the current in the circuit and cause all the bulbs to be
dimmer
- if one bulb burns out, the circuit is open and electric charges can’t flow so all the bulbs go out
- parallel circuit – electric charges have more than one path they can flow
- loads are connected side by side
- any bulb can burn out without opening the circuit
- loads can have different currents even though all experience the same voltage
- all bulbs will glow at the same brightness, even when more bulbs are added in
- How to use electricity safely
- avoid exposure to the current
- the minerals dissolved in the water in your body makes your body a good electrical
conductor – stay away from electricity or you can get burned, shocked, or even die
- SAFETY PRECAUTIONS
- never use electrical devices around water (don’t have your ipod in the shower with you)
- don’t use any appliance if its power cord is worn or damaged
- always pay attention to warning signs near places with high-voltage transmission lines
(you can get a shock by coming near them – you don’t have to actually touch them)
- use electrical safety devices
- fuses, circuit breakers, and ground fault circuit interrupters (GFCIs) are safety devices
that act like switches and turn off the electrical devices when the current is too high
- take precautions during lightening storms
- stay away from trees and other tall objects during thunderstorms since lightening will
usually strike tall objects first
- don’t stand up in the middle of a field in a thunderstorm and don’t stand on tree roots –
the lightening can travel through the tree and get you when you’re standing on a root
- lightening rods are placed on many tall building to ground the electrical charge when it
gets hit
Lesson 4 – Magnets and Magnetism
Essential Question: What is magnetism?
By the end of this lesson, you should be able to describe magnets and magnetic fields and explain their
properties.
- magnet - any material that attracts iron or objects made of iron
- many made of iron, nickel, cobalt, or mixtures of these metals
- magnetic force – push or pull created by two magnets close to each other
- force comes from spinning electric charges in the magnets
- force can either push the magnets apart or pull them together
- acts at a distance – doesn’t need to touch something to attract or repel it
- magnetic poles – ends of the magnets that push or pull against each other
- every magnet has a north end and a south end
- the same poles turned towards each other will repel and opposite poles turned towards each
other will attract
- magnetic field – area surrounding a magnet where magnetic forces can be detected
- arranged in lines that enter the magnet at the south pole and exit the magnet at the north pole
- strongest near the poles
- the greater the distance from the poles, the weaker the magnetic field
- if you place a magnet down in metal filling, the fillings will line up to visibly show the magnetic
field
- Whether a material is magnetic or not depends on the material’s atoms
- as electrons move in an atom, they make a magnetic field
- the electron then has a north & south magnetic pole
- in most atoms, like copper and aluminum, the magnetic fields of the individual electrons cancel
each other out – these materials aren’t magnetic
- the electrons in iron, nickel, and cobalt do not completely cancel each other out – these
materials have a small magnetic field
- if you cut or broke a magnet into two pieces, each piece would be a magnet with a north & south
pole
- no matter how many pieces you break the magnet into, each will have a north & south pole
- domains – like tiny magnets within an object that line up and make a stronger magnetic field
- determine whether an object is magnetic
- when a magnetic material is placed within a magnetic field, most of the domains point towards
the same direction, forming a magnetic field around the entire object
- if there are no domains to line up then the material can’t become magnetized and become a
magnet
- ferromagnets - a material that can be turned into a magnet
- nickel, iron, cobalt, or mixtures of these materials, have strong magnetic properties & are
considered ferromagnets
- can be turned into a permanent magnet when placed in a strong magnetic field
- permanent magnets are hard to make but keep their magnetic properties longer
- magnets come in many different shapes and sizes
- electromagnets – iron core wrapped with electrical wire
- current runs through the wire creating a magnet only when the current is turned on; as soon as
the current is turned off, the magnet is turned off
- the strength depends on the electric current
- temporary magnets – magnet for a short period of time when the domains line up and are magnetized
- to make one, rub one pole of a strong magnet in one direction on a magnetic material (like a pair
of scissors); domains line up for a short period of time and the scissors become a magnet until
the domains lose their alignment
- banging or dropping a temporary magnet will also cause it to demagnetize
- Earth acts like a giant magnet and has a magnetic field
- Earth’s magnetic poles attract another magnet, like a needle of a compass
- as Earth rotates, it’s outer core (liquid iron and nickel) moves creating a magnetic field
- the constant rotation keeps Earth magnetized
- Earth’s magnetic and geographic poles are different from each other
- Earth’s geographic poles are at the ends of Earth’s axis
- the “north pole” of Earth is actually the south end pole since the north end of a magnetic is
attracted to it
- Earth’s magnetic fields flip over time and the north and south poles change places
- this is seen in the lining up of the domains in the rocks as they are created over time
- aurora – beautiful display of lights that is seen at northern or southern latitudes
- the sun ejects particles that push in Earth’s magnetic field and enter Earth’s upper atmosphere
near the magnetic poles
- when the charged particles interact with atoms in the air, it causes the atoms to emit visible light
- in the Northern Hemisphere it’s called an aurora borealis; in the Southern Hemisphere it’s called
the aurora australis
Lesson 5 – Electromagnetism
Essential Question: What is electromagnetism?
By the end of this lesson, you should be able to describe the relationship between electricity and
magnetism and how this relationship affects our world.
- electromagnetism - when electric currents and magnetic fields interact with each other
- relationship between electricity and magnetism
- 1820, physicist Hans Christian Oersted discovered there is a connection between electricity and
magnetism
- brought a compass close to a wire carrying an electric current & compass needle moved
- compass needle is a magnet and usually points north due to Earth’s magnetic field
- in this case the compass moved because it was affected by a magnetic field created by the
electric current flowing through the wire
- Oersted’s experiments proved that a magnetic field is produced around a wire when the wire is
carrying a current and is gone when the current is turned off
- current in one direction causes the compass needle to move clockwise & current in the other
direction caused the compass needle to move counterclockwise
- solenoid – coil of wire that carries an electric current and makes a magnetic field
- the more loops, the stronger the magnetic field
- more current, the stronger the magnetic field
- the magnetic field acts like a bar magnet
- electromagnet –a solenoid wrapped around an iron core
- combines the magnetic field of the solenoid with the magnetic field of the magnetized iron core
- makes a more powerful magnetic field than the solenoid alone
- make it stronger by adding more loops to the solenoid or by increasing the electric current
- uses of electromagnets
- solenoid around an iron piston make a doorbell ring
- huge electromagnets are used in industry to move metal
- small electromagnets drive electric motors in everything from hair dryers to speakers
- physicists use electromagnets in “atom smashers” to study the parts of an atom
- electromagnets are used to move things, like the maglev train which is suspended above the train
tracks my magnets and powered by magnets – they are the fastest trains in the world
- galvanometer – device that measures the strength and direction of an electric current in a wire
- contains an electromagnet between the poles of a permanent magnet, like a horseshoe magnet
- when current is applied to the electromagnet, the two magnetic fields interact and cause the
electromagnet to turn
- the indicator attached to the electromagnet moves to one side of the zero on the scale, indicating
the strength and direction of the current
- Magnetic resonance imaging (MRI) machines use powerful electromagnets and radio waves to see
inside the human body
- in most machines the solenoid coils are kept at temperatures around -452 °F (-269 °C)
- helps doctors understand how the brain works
- used to diagnose many different things, like broken bones and strained tendons
- electric motor - device that changes electrical energy into mechanical energy
- contains an electromagnet in the motor
- some run on direct current (DC), and other use alternating current (AC)
- used to power everything from a Ferris wheel to small motors found inside tiny fans in
computers to keep them cool
- electromagnet inside the motor needs to rotate all the way around inside the magnetic field
- simple motor has a coil or loop of wire called an armature between the poles of a magnet
- the armature becomes an electromagnet when current passes through the opposite poles
of the magnet
- the armature rotates because the poles are pushed & pulled by the opposite poles of the
magnet
- the commutator reverses the direction of the current so the north pole of the armature can
continue to turn all the way around inside the magnets
- Michael Faraday, an English scientist, showed that a magnetic field could create an electric current
- connected a galvanometer to a wire coil & moved a magnet back and forth inside the coil; the
galvanometer needle moved showing there was an electric current
- Joseph Henry, and American physicist, made a similar discovery to Faraday
- electromagnetic induction – when a magnetic field is used to create an electric current in a wire
- the magnetic force from a magnet moves inside a coil of wire makes the electric charges in the
wire move
- when the magnet stops moving inside the coil, the electric current stops
- transformer – uses electromagnetic induction to increase or decrease the voltage of alternating current
- transformers on power lines increase voltage to send it miles away and then decrease voltage
before sending it into a single home
- most are iron rings with two coils of wires; the wire on the primary side makes an electromagnet
& because the current alternates, the magnetic field changes which induces a current in the wire
on the secondary side
- electric generators – use electromagnetic induction to change mechanical energy into electrical energy
- essentially the opposite of electric motors
- uses mechanical energy to rotate turbines which turn magnets inside coils of wire generating
electricity
- many power plants use rising steam to turn the turbines; steam is made by burning fossil fuels
or using nuclear reactions to heat water
- blowing wind, falling water, and ocean tides and waves can also turn the turbines
- generators induce electric current when a magnet moves in a coil of wire or when a wire moves
between the poles of a magnet
Lesson 6 – Electric Technology
Essential Question: What are electronics, and how have they changed?
By the end of this lesson, you should be able to describe what electronic devices do and how they change
as technology changes.
- electronic device – able to control the flow of electrons using integrated circuits
- different from electrical devices that also use electrical energy because electronic devices
control the flow of electrons
- ex: TV remote control
- integrated circuit (microchip) – is a single, tiny chip of specially treated silicon containing many
circuit parts
- carry out instructions, or programs, by controlling current
- analog signals – signals that change continuously in a given range
- ex: dimmer switch sends an analog electrical signal to the light fixture to make the level of light
increase or decrease
- dimmer switch is slid up and down in one continuous motion which raises or lowers the
amount of electric current supplied to the light
- ex: record also makes an analog signal that the needle on the record player reads as it moves
across the grooves of the record
- the up and down movements are turned into sound waves by the record player & as the
grooves change, the sound changes
- digital signal – a sequence of separate vales
- goes back and forth between on and off
- information is represented using a pattern called binary code
- binary code if made up of two digits 1 & 0 (on & off)
- carried by series of on-off electric pulses with “1” being a pulse & “0” as no pulse
- computer - any electronic device that performs tasks by following instructions given to it
- receive information, called input, through keyboards, touchscreens, or other devices
- input is processed through a central processor or stored in memory
- output is delivered through monitors, printers, or other devices
- changed greatly over time
- ex: smartphones, camera, ipods, ipads, laptops
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current x resistance