Physics - Electricity Lessons 1-12

Lesson 1 - Static electricity

Electrostatics 

• Study of static electric charge 

• All matter is made up of extremely tiny particles called atoms

• Atoms are made up of three subatomic particles 

  • Protons with a positive charge

  • Neutrons with a neutral charge 

  • Electrons with a negative charge but also can be transferred 

Atom 

Neutral atom 

• 6 electrons shown

• No electric charge 

• Thus 6 protons 

May form an ion 

• Gain electrons which are negative

  • Anion

• Lose electrons that are positive 

  • Cation 

Static electricity 

• A stationary electric charge 

• Created when the atoms make up an object gain or lose electrons 

  • Become ions 

Electric charges 

• Positive charge 

  • Attracts negative and neutral objects 

• Negative charge 

  • Attracts positive and neutral charge 

• Neutral or uncharged 

  • Attracts positive and negative objects 

Law of electric charges 

• Like charges repel one another 

• Unlike charges attract one another 

Creating an electrostatic charge (3 ways)

• Friction

• Direct contact

• Induction 

Transferring electrical charges 

Friction 

• An object rubs against another transferring object charge 

• Example- rubbing a balloon with a piece of silk 

Tendency to be static

• An electric charge that stays where the friction occurred on the charged object 

Direct contact 

• Object touches another transferring charge 

• Example- a negatively charged person touching a neutral door knob

Charging by induction- temporary 

• A charged object approaches a neutral object 

• Causing the similar charge in the neutral object to move in an opposing direction 

• Thus causing a temporary charge 

• For example - a negatively charged balloon approaches a neutral charged wall

The electrostatic series 

• List of objects or materials ranking their ability to lose electrons 

  • The higher on the list the object is more likely to lose electrons 

    • To become positively charged 

• Friction between objects causes the transfer of electrons 

Example 

• If you rub together a rubber balloon and your hair, how will electrons travel 

• Since hair is higher on the list it will lose electrons 

  • Hair is positive 

  • Balloon is negative 

human skin

leather

rabbit fur

glass

quartz

hair

nylon

wool

cat fur

silk

aluminum

paper

cotton

steel

wood

amber

copper

silver

gold

polystyrene

cellophane

PVC

silicone

Teflon

rubber

Insulator 

• Electrons are trapped on individual atoms

• If you add electrons to the atoms they will stay there

• Removed only by contact with materials less likely to hold electrons 

Conductor 

• Electrons can move freely between atoms on the object 

• When electrons are added they will flow through the object to the area of the greatest positive character 

• Used as grounds

  • Ground wire 

• Allows electrons to enter or leave to neutralize object 

Conductors 

Good: silver, copper, gold, aluminum, magnesium, tungsten, nickel, mercury, platinum, iron

Fair: graphite (carbon), nichrome, the human body, damp skin, acid solutions, saltwater, Earth, water vapour

Lesson 2 - Charging by friction

Charging 

• Unequal number of positive and negative charges 

Charging by friction 

• Transferring an electric charge from one substance to another by rubbing action 

• Example- walking across carpet wearing socks 

Review - Atomic structure 

• Protons say in the nucleus 

  • They don’t move

• Electrons are free to move

  • They can be transferred to different objects 

• Example- coming hair with a plastic comb

  • Electrons were transferred while protons stayed in their original positions 

  • The comb had a stronger attraction for electrons than hair

Electrostatic series 

• Can be used to determine the kind of electric charge produces when two substances are rubbed together

Chart of electrostatic series 

How does it work?

• The top of the list has a weaker hold on electrons 

  • The objects want to give away their electrons 

• Electrons are negatively charged 

  • If the object gives away negative it becomes positively charged

• The bottom of the list has a stronger hold on electrons 

• Objects want to keep their electrons 

  • They will attract any other electros from other objects with weaker abilities 

• Electrons are negatively charged if it adds more to it then it will stay as negatively charged 

• For example - if silk and acetate are rubbed together 

  • Silk has a stronger hold on electrons 

  • Electrons are transferred from the acetate to the silk

Lesson 3 - Insulator and conductors

Insulators 

• Is a substance in which electrons cannot move freely from atom to atom

• Gains electrons it becomes negatively charged 

• The charge will continue to build-up 

• Used to protect us from electric shock

Examples of insulators 

• Oil 

• Wood

• Glass

• Plastic

• Rubber

Conductor 

• Is a substance in which electrons move freely from one atom to another

• If the conductor is charged with extra electrons 

  • They will move freely along the conductor 

Examples of conductors 

• Copper

• Aluminum 

• Gold

• Platinum

• Saltwater

• Human body

A good insulator is a poor conductor

• Example - wires 

• Conductor = aluminum or copper wire

• Insulator = rubber or plastic layer

Discharging objects 

• Objects can become charged with excess electrons

• When electrons are removed from the object 

  • They are discharged or neutralized 

• Several ways of doing this 

  • Grounding - once connected to the earth, the earth can take all extra electrons 

    • Rapid grounding results in sparks

  • Discharge at the point - electrons repelled until they reach a point and repelled into air

Lesson 4 - Current Electricity and Circuits

What is current electricity 

Static electricity 

• Electrons build up in one place 

• Move randomly 

• Can travel short distances by discharge 

Current electricity

• Electrons flow through a conductor 

• Move-in a controlled way 

• Can travel long distances 

Electron flow in a conductor 

• For an electron to flow, a source of energy is needed 

• Example - battery 

  • When it is charged, electrons will flow

  • When it is dead, electrons don’t flow

Conductors and insulators 

Conductors 

• Materials that allow electrons to flow easily 

  • Examples- 

  • Metals

  • Saltwater

  • People

  • Animals

Insulators 

• Materials that don’t let electrons flow easily 

• Examples -

• Rubber

• Plastic

• Fabric

• Glass

• Wool

• Wood

Electric circuits 

• Is a continuous path for electrons to flow

• Example- electrically moving through a wire

Incomplete circuit/ open circuit 

Complete circuit/ closed circuit 

Components of a circuit

• The simple circuit consists of…

• Source

• Connectors

• Control devices

• Loads

Sources 

• The energy source is the beginning of the electric circuit pathway 

  • Gives electrons a push

• Electrons leave through the negative end of the source

  • It will return to the positive end

  • Basically, they will go in a circle!

Connectors 

• Are conductors such as wires

• Usually made of copper and aluminum

• Join all parts of an electric circuit together

Control devices 

• Manage the flow of electrons

• Example - switch for a light bulb

• Switch is ON

  • Circuit is closed

  • Complete path for electrons flow

  • Energy lights up the light bulb

• Switch is OFF

  • Circuit is open

  • Incomplete path for electron flow

  • Bulb will not light up

Loads 

• Is a device that transforms electrical energy into other usable forms of energy 

• Examples

• Light bulb - light energy

• Heater - heat energy

• Speaker - sound energy

• Fan - mechanical energy

Short circuit 

• Occurs when the electric current has found a shorter path to return the source without going through an appropriate load 

• This causes the battery to become dangerously hot

• Could cause the battery to burst 

Sources of electrical energy 

Comes from different sources

• Electric cells 

• Portable devices that convert chemical energy into electrical energy 

• Example - batteries 

• Non-rechargeable is called primary cells 

  • When chemical reactions stop, the battery is dead 

• Rechargeable is called secondary cells

  • These batteries last much longer than primary cells

• Fuel cells 

  • Special kind of electric cell that continually produces electricity along as a fuel source is provided 

  • Example - hydrogen 

Electric VS fuel cell vehicles 

• Electric vehicles

  • Energy is stored in batteries to power one or more electric motors 

• Fuel cell vehicles 

  • Hydrogen is stored in a fuel cell in the car 

  • Reacts with oxygen from the air to create electricity

Lesson 5 - Series and parallel circuits 

Circuit diagrams 

• Is a way of drawing an electric circuit using standard symbols 

• Negative and positive signs are used to identify the two terminals of an energy source 

Cell vs battery

• Cell 

  • Is a single unit that converts chemical energy into electrical energy

• Battery

  • Is a collection of cells

  • 9 volt battery is actually a collection of 6 1.5 volt cells wrapped together

Series vs parallel circuits 

• Most circuits are used in everyday life have more than one load 

• The loads may be connected in 2 ways

Series circuits 

• Loads are connected in a chain that forms a loop

• Electrons flow one path

• Loads are connected one after the other in a chain that forms a continuous loop

• All electrical devices must be on or off at the same time

• Example - flashlights, cordless tools

Parallel circuits

• Loads are connected on different branches of wires

• Electrons flow in more than one way

• Loads are on at least 2 different branches of wires that connect to an energy source

• Each electrical device can be on or off with the same circuit 

• Examples - household wiring, stereo speakers 

Series or parallel 

• A good example of examining circuit types is to remove 1 Christmas tree bulb from a string of lights 

• If the entire string of lights goes off

  • Is a series circuit 

• If remaining lights stay on after one is removed

  • Parallel circuit 

Simple circuit diagrams 

• The switch can go anywhere as long as it makes sense

• The battery can go anywhere but keep it on the outside for parallel circuits 

• Certain types of batteries are called dry cells

Lesson 6 - Electric current 

Electric current 

• For any electrical device to operate

  • There must be a flow of electrons 

• When electrons flow through a conductor 

  • It is said to constitute an electric current 

• Electric current is the rate of electron flow in a circuit 

• The faster the electric charges travel through the conductor 

  • The greater the current

• Electric current is measured in amperes (amps)

Measuring current 

• When an electrical circuit stops working

• An electrician is called 

• Electrician use an ammeter to measure the current flowing through different loads on a circuit

Ammeter 

• Must be connected in series with a load to measure the current flowing through the loads 

• Ensures that all the electrons that flow through the load (ex. lamp) will also flow through it

Safety with electric current 

• Very large currents can damage ;electrical devices 

  • Causing a electrical fire

• This is why every home has a distribution panel with circuit breakers 

  • Fuses in older homes 

• Too much current going through the circuit breaker causes it to trip 

  • Behave like an open switch so that no current can flow through it

Lesson 7 - Potential difference 

Potential energy 

• Is the stored energy an object has because of its position or state 

Examples 

• Bicycle on top of a hill

• Book held over your head 

• Stretched elastic band 

Kinetic energy 

• Is the energy of motion

• When potential energy is used it is converted into kinetic energy

• You can think of potential energy as kinetic energy waiting to happen

Model of potential energy 

• For centuries people have used the energy of falling water to push waterwheels 

• Is possible 

  • Water above the wheel has more gravitational potential energy than it does below the wheel

  • As the water falls, it moves from an area of high potential energy to an area of low potential energy 

Potential difference 

• Similar to the flow of water 

• Electric charges will flow from a point of higher potential to a point of lower potential 

• This difference in electric potential between 2 points in a circuit is known as the potential difference

• We often refer to potential difference as voltage 

Electron flow in a battery 

• In battery

  • Electrons flow from the negative electrode ( higher potential energy) to the positive electrode (lower potential energy)

Measuring potential difference 

• When an electrician, technician, or engineer troubleshoots a circuit

  • The voltage, as well as the current at different parts of the circuit, must be measured 

  • A voltmeter is used to measure potential difference 

Voltmeter vs ammeter 

• The voltmeter must be connected in parallel with a load or an energy source

• The ammeter must be connected in series 

• The reason for this is voltage is relative to two points 

• There is always a drop in voltage across a load or energy source

• Example

  • To measure the voltage across the lamp in the figure shown

    • Connect the voltmeter in parallel with the lamp

  • The negative side of the battery is connected to the negative side of the voltmeter

Lesson 8 - Resistance 

Resistance in circuits 

• Is the opposite of electrical conductivity 

• Is the ability of a material to resist the flow of electrons as they move through a circuit 

• Uses the symbol R for resistance

• Is measured in ohms (Ω)

Model for resistance

• Example of kicking a soccer ball

• If the ball is on a smooth, hard surface like pavement the ball will roll easily

• If the ball is on a rough surface like tall grass, you would have to kick the ball much harder just to make it roll

• In the same way

  • Electrons flow through a material that might be smooth or rough

Internal resistance 

• All materials have some of this

• Greater resistance lowers the current 

• The warmer the material becomes when current flows through it

• This happens because

  • Electrons move through the material they bump into the atoms that make up the material

• The material becomes warm because electrical energy is being converted into thermal energy 

• Many devices that we use everyday use materials with high internal resistance

• Example- toaster consists of nichrome wires

  • Which have a high internal resistance

• The electrical energy through the wires gets converted into light (the red glow) and thermal energy

• Thermal energy is what toasts the bread

Factors that affect resistance

Type of material

• Materials are good conductors have a low internal resistance 

  • Example - copper wire, electrons flow freely 

Thickness of material 

• Thicker the conducting wire, the more room for electrons to flow, less internal resistance

Length of material 

• The longer the wire, the greater the internal resistance, the electrons have to travel through more material

Temperature of material 

• Resistance increases as temperature increases

Resistance in circuits 

• When electrons move through an electrical circuit 

  • They meet up with a load (ex. light bulb) causing resistance

  • Tries to stop the flow of electrons

• Resistance from the bulb converts the electric current into heat energy

• Filament becomes so hot that it glows

• Conversion of energy causes electrons to lose much of their energy

• Is called voltage drop 

  • Voltage is lost or dropped across a conductor 

Measuring resistance

• Just as current and voltage are useful quantities to measure when troubleshooting a circuit, so is resistance 

• Ohmmeter measure resistance

• Ohmmeters are placed in parallel with a load

Resistors in circuit 

• The resistor is any electrical device that reduces the current in a circuit

• Examples 

  • Dimmer switches

  • 3-way lamps 

  • Volume controls on stereos 

  • Internet modems 

  • Cell phones 
    

Lesson 9 - Ohm's law

Ohm's law

• Is the mathematical relationship between the current, potential difference (voltage) and resistance

Ohm’s law states

• If the voltage increases, the current increases

• If the resistance decreases, the current increases

V is the voltage

I is the current

R is the resistance

How does it work

• An electric circuit is formed when a conductive path is created to allow free electrons to continuously move

• Force that is motivating the flow of electrons is called voltage

• It is a specific measure of potential energy that is always relative between two points

• Free electrons tend to move through conductors with some degree of friction, or opposition to motion called resistance

Applying ohm’s law

• Using this law we are able to analyze electric circuits

• If you know any two values, you can analyze the third one

Lesson 10 - Kirchhoff's laws 

Total resistance

• If you have a circuit with 1 load the total resistance of the circuit will be different than if you have 2 or more of those loads connected in series or parallel

• The current flowing through a circuit with multiple loads will be less than the current flowing through a circuit with 1 load

• Adding more loads to a circuit increases the total resistance of the circuit 

  • This affects the intensity of light bulbs in the circuit

• As more bulbs are added, the dimmer the light bulbs will glow because there is less current going to each bulb

• However, all the bulbs in each arrangement will glow the same

Kirchhoff’s laws

• These laws explain the relationship between current, voltage, and resistance, as they apply to series and parallel circuits

• Current law

  • All current that enters a loop, exit that loop

• Voltage law

  • The sum of the voltage within a loop equals the voltage at the source

Series circuit 

• No matter how many loads are connected in series, there is only one path that the current can follow

• If one light bulb goes out, the remaining light bulbs go out

Series circuit - current 

• Current is the same between any 2 points measured total = I1 = I2 = I3, where I is the current measured in amps.

Series circuit - voltage 

• The voltage at the course will equal the sum of the voltages across all loads

• Vtotal =  V1 + V2 + V3 , where V is the voltage measured in volts.

Math formulas 

• It is easier to simplify these formulas when using then in tactical applications

• You will have to rearrange the formulas as needed for each circuit problem

Example for series circuit - math

Parallel circuit 

• When you connect loads in parallel, there are multiple paths the current can follow 

• If one light bulb goes out, the remaining light bulbs stay lit

Parallel circuit - current

• The current is the sum of all current at each junction 

• Itotal =  I1 + I2 + I3, where "I" is the current measured in amps.

Parallel circuit - voltage 

• The voltage at the course will be the same across all loads

• Vtotal =  V1 = V2 = V3 , where V is the voltage measured in volts.

Math formulas 

• Is it easier to simplify these formulas when using them in practical applications?

• You will have to rearrange the formulas as needed for each circuit problem

Lesson 11 - Current and voltage analogies 

Electric current 

• Is the rate of flow of electrons in a circuit

• Current can be compared to the flow of water in a river

• Series circuit

  • The rate of flow is the same anywhere throughout the circuit

• Parallel circuit 

  • The rate of flow along every parallel path adds up to the rate of flow at the battery

Voltage 

• Is the potential to do work

• Can be compared to the amount of money you have to spend 

• Series circuit

  • The volts are shared throughout the whole circuit.  For example, if a battery produces 20 Volts, every light on the circuit must share that potential energy.  Similarly, if you have $20, you have to spend a little of it at every store you visit (and return home with no extra money).  This means all lights will be relatively dull because they are all sharing the volts

• Parallel circuit 

  • Each pathway gets the same amount of voltage because the electrons can only take one path.  Similarly, if you have $20 each pathway gets $20 and it does not need to be shared.  This means all lights will be very bright

Lesson 12 - Energy at home 

Electrical power 

• Is the rate at which electrical energy is produced or consumed in a given time

• Unit of measurement for electrical power is the watt (W)

• One watt is the equivalent of one joule per second (J/s)

• Higher the power rating value, or wattage the more electrical energy a device produces (or uses to operate)

Light bulbs and power 

• Consider a 60 W incandescent light bulb and a 15 W compact fluorescent bulb (CFL)

• The incandescent bulb uses more electrical energy than the CFL bulb to produce light

• Each produced about the same amount of light 

• In the incandescent bulb has extra energy 

  • It turns it into thermal energy instead of light

Measuring electrical energy 

• Joule is a relatively small unit of electrical energy so we often measure larger amounts of electrical energy

• Kilowatt-hour is the SI unit used to measure energy usage 

  • It is the use of one kilowatt of power for 1 hour

• Electrical meters keep track of how much electrical energy is used in home, schools, and businesses in units of kWh

Transfer of energy 

• Total energy that goes into a device is always equal to the energy that goes out 

• Energy going into an electrical device is called energy input 

• Energy going out of the electrical device can be both useful energy and wasted energy

Energy efficiency 

• Useful energy is the energy we want the device to produce 

• In a light bulb, this would be light energy

• Wasted energy is energy lost to its surroundings which are thermal 

• Efficiency refers to how well the electrical energy is changed into useful energy by a device

• The energy efficiency of this incandescent light bulb is only 5%

Energuide and energy star 

• all households appliances are sold with an Energuide label which estimated how much electrical energy appliances use 

• Some appliances are labelled with the energy star symbol which indicated that a product meets or exceeds high-efficiency standards 

Energy-efficient homes 

• Our houses need to be heated in the winter and cooled in the summer 

• We turn lights on and off

• We use appliances 

• Electrical usage in the home costs money (sometimes a lot)

• Newer homes are built more energy efficient

• It Helps reduces electrical costs by reducing the amount of energy required to operate the home

Make a home energy efficient

Calculating efficiency 

• The higher the percentage, the more efficient the device is

• Can calculate the efficiency of a device using equation

• Percent efficiency = energy out/energy in x 100%