Electricity

Grade 9

Electricity

The movement or flow of electrons

Law of Charges

Like charges repel and unlike charges attract

What do uncharged or neutral atoms do?

They attract others

How does static work?

A build-up of charges causes unbalances and electrical discharge causes the shock

Electrical Discharge

The rapid re-balancing of charges

When a balloon and hair have static electricity how is the balloon charged?

The balloon has a negative charge while the hair has a positive charge

How is electricity like water flowing in a waterfall?

Current- The water

Voltage- The height of the waterfall

Resistance- The rocks (slows down the water)

Current

The continued flow of electrons

What is the relationship between voltage and electrons?

Voltage is the force of push on the electrons moving through a circuit

Resistance

The difficulty or slowing of a current

Grounding

We use electrons to move through wire to the ground (Earth can absorb re-donate electrons without becoming unbalanced)

Conductor

Any material that can allow transfer and passage of electrons

Examples of good conductors

Gold, aluminum, silver, copper

How do conductors work?

They hold their electrons loosely and can allow electron flow

What do we use conductors for?

To make wires and things that need electricity

Easy electron flow=

Low resistance

Semi-Conductors

• Metalloids

• Medium resistance

• Used in energy conversions

(e.g. LED lights, microcontrollers, transistors)

Insulator

Any material that blocks the transfer and passage of electrons

How do insulators work?

They hold electrons tightly

What do we use insulators for?

To wrap wires and block harmful flow

Examples of insulators

Wool, rubber, plastic, wood, paper

Circuit

Allows the passage of electrons through a specified path

Open circuit vs Closed circuit

An open circuit does not allow electron flow, a closed circuit does

Series Circuit

• Current flows through each component one at a time in a series

• Current always stays the same BUT voltage lowers across each load

-Easier to construct

-Fewer materials

-If one thing breaks nothing works

Parallel Circuit

• Current passes through multiple paths (current is divide between the different paths)

• Voltage is constant across each load

-Each component can be controlled individually

-More energy is required

Cell

2-Cell (battery)

Light bulb

Amperemeter/ammeter

Volt meter

Resistor

Closed switch

Open switch

Conductor (straight line)

Motor

Fuse

General load (e.g. light, heater, speaker, etc.)

In which directions do electrons flow to and from in a circuit?

From the negative terminal to the positive terminal through the circuit

Voltage

The difference in potential energy

What units is voltage in?

Volts (V)

How does voltage have to be measured?

Voltage must be measured between 2 different points on a circuit (across something)

Where is there a decrease or increase in volts across a circuit?

Increase in volts across a cell ro battery and a decrease across charges

What is the unit and symbol for current?

Unit: Amps (A)

Symbol: I

Resistors

Slows down the flow of the current

What is the unit for resistance?

Ohms (Ω)

Ohm’s Law

For a given conductor, the ratio if voltage to current (^v/_I) is CONSTANT

What is this?

The relationship between voltage and current

Typically, high voltage= high current

What is the formula for resistance?

R= ^V/_I

What is the formula for voltage?

V= R x I

What are some factors that affect resistance?

• Material

• Length

• Temperature

• Diameter

How are home circuits wired?

In parallel- can use a lot of energy which can be a fire hazard

Fuses

A thing metal strip, all fuses have a low melting point and when there is too much heat the fuse will break first

What is this?

A blade fuse

What is this?

A cartridge fuse

What is this and how does it work?

Bimetal Strip, When the circuit is not overheated, the strip is straight but if the circuit does overheat the strip bends flipping a switch and disrupting the circuit

Efficiency

the measure of how much energy is used and turned into useful energy

What is the formula for efficiency?

E= ^O/_I x100

Why is tungsten used as a filament in incandescent light?

It resists the flow of energy

What do variable resistors do?

They control the flow of current (amount)

How can the resistance of a wire be reduced?

By increasing the diameter of the wire or decreasing the length

mA

milli Amps (0.001 Amps)

What is the relationship between generators and motors?

They are opposite, generators get electric energy from kinetic energy and motors get kinetic energy from electrical

Alternating current (AC)

Electrons flow in alternating directions and a regular pattern

Direct Current (DC)

Electrons flow through a circuit in one direction (continuous or in pulses)

Use this diagram to explain electromagnetism

A magnetic field forms around metal when a current passes, it becomes electromagnetic (the more coils in the metal and the high voltage/current the better)

What is this?

A DC generator

Explain the diagram

• A DC Generator

• SPLIT ring causes circuit to break so that electrons pulse in one direction

• The wires move back and forth between magnets

• We rotate the crank

How does an AC generator work?

About the same as a DC one but with either not split ring or two split rings

Explain how a St. Louis motor works

A motor works when an electrical circuit is complete and electrons flow throughout. A commutator begins to spin and creates electromagnetism, the field magnets are repelled by the permanent ones and eventually when it reaches the split in the ring the poles changes and that forces of repulsion and attraction continues.

Electrochemical cells

Cells that transform chemical energy into electrical energy

What do two cells contain?

2 electrodes (cathode and anode)

Electrolyte (ionic compound/acid)

Label the diagram

Describe the properties of a dry cell

• Safer

• More portable

• Barely leaks unless electrode degrades

Describe the properties of a wet cell

• Easily spills

• Can be corrosive when it leaks

  • Easy to happen

What is this?

A wet cell

Electro chemical cells work best when?

• More surface area of electrodes in the electrolyte

• High concentration of electrolytes

• 2 different metals for electrodes

Electrochemical cells do not work well when?

• 2 of the same metal

• Molecular solution

How do electrochemical cells work?

Electrons flow from the anode to the cathode THROUGH the conductor (eventually the anode gets “used up”)

Rechargeable cells

We feed electrons to the cell, as we use an anode that can be “rebuilt” and can be used again (still not a renewable resource)

Non-rechargeable cells

Most cells, once the anode is used up the cell is useless

Microbial Fuel Cells

Different microbes can emit/release electrons when they consume/process nutrients in the soil (atoms, compounds, ions)

Explain this diagram

Electrons from the cathode come through the circuit, microbes process nutrients in the anode and deposit electrons for the circuit.

What is this?

A car battery

Wha are the properties of a car battery?

• Lead battery

  • Made of the element of lead

• Uses a strong acid

• Unsafe and corrosive

Renewable energy source

Can be used/regenerated in a sustainable manner

Solar energy

We use photo-electric cells, sensitive to radiation energy (Radiation → Electricity)

Cons of solar energy

• Not always reliable (depends on the weather)

• Space (solar farms)

• Expensive and insufficient

Wind turbines

The wind will push a turbine, which is a generator

Cons of wind turbines

• Kills birds and bugs

• Not always reliable (depends on weather)

Hydropower

Moving water will push a turbine, which is a generator

Cons of hydropower

• Hazardous to marine life

• Space

• Flooding concerns

Geothermal energy

The use of heat from Earth’s mantle (from 30m to 120m)

Cons of geothermal energy

• Only viable where we can dig and access geothermal vents (not an issue in Alberta)

Biomass/Bio fuel energy

“Burning” (Incinerating) organic matter to get energy

Cons of biomass/ bio fuel

• Pollution/danger if we mess up

• Expensive and hard

Nuclear power

A reactor performs fusion and fission to heat water, which creates steam which rises and spins a turbine

Cons of nuclear power

• Space

• Nuclear meltdown/fallout concerns

• Concerns with waste management

• Environment and health

SUSTAINABLE BUT NOT RENEWABLE

How can we increase sustainability?

• Turn off devices

• Wear a sweater or blanket

• Use mass transportation

• Insulate home

• Double paned windows

Non-Renewable Energy Resources

These sources either cannot be replenished sustainability or at all

Coal

Produced from fossilized plants and trees from roughly 300 million years ago- abundant in Alberta (cheap and our primary energy source) AKA “dirty” energy