Current Electricity and Circuits

• Electricity is a form of energy

• Electricity can exert a force on other objects

• Think of your Laws of Charge activity

• Electricity is when electrons flow

What is electricity?

• Electrons are held very loosely by the nucleus.

• This means an outside force that ‘pushes’ the electrons can cause them to move from one atom to another

• The resulting effect is electricity.

How do electrons flow?

• We already know some materials can move electrons better than others • Think of static electricity-some materials lost electrons easier

because their electrons can move more easily.

• Materials that move electrons easily are called conductors• These materials have the physical property of being electrically

conductive

• Hold electrons loosely

• Typically metals

• Materials that do not move electrons are called insulators• These materials are not electrically conductive

• Hold electrons tightly

• Typically non-metals

Conductors and Insulators

• All Energy has to follow the 1st Law of Thermodynamics

“Energy Cannot Be Created or Destroyed, Only Transformed from One Form Into Another”

• Since electricity is energy, it means we can’t ‘make’ electricity

• We can change other forms of energy (heat, light, motion, etc) into electricity

Energy

• In static electricity, we saw electrons flow from one object to another• This electricity built up on the surface• It didn’t move through the material (that’s

why it’s called static)

• Current electricity is when electrons flow through a material.• Current electricity has a continuous flow

of electrons• Current electricity is what we use to power

our homes,

run our electronics, etc.

Static Electricity

• Current Electricity is what is typically thought of as the most useful type of electricity

• It is what powers our homes, what is created by batteries, and is what we typically use in everyday life.

• This is because it is easy to change current electricity into useful forms of energy

• Electrical energy is not useful on its own • Except for things like tasers and electric

fences

• Electricity is very useful when we convert electrical energy into light heat or motion

Current Electricity

Voltage is the energy per unit of charge. So what does that actually mean?

• You can think of voltage as if it were the amount of ‘push’ that is given to electrons.

• Voltage gives electrons energy to move

• Measured in Volts (V)

Voltage

• As you give electrons a push to the next atom, it leaves a positive charge behind.

• The electrons (negatively charged) are attracted to the positive charge that was left behind.

• As electrons keep getting pushed forward, they leave positive charges

• Electrons keep moving towards the positive because they are attracted

Voltage

• The higher the voltage, the more push

• This is why more volts makes lights look brighter, heaters hotter, etc.

• Voltage is a lot like pressure (how much push you give water)

• Good conductors don’t need much voltage to move electrons because their electrons are held loosely

• They need less push to move

• Insulators need huge amounts of voltage to move electrons because their electrons are held tightly

• They need a lot of push to move

Voltage

• Current is how fast electrons move through a material

• This depends on the properties of the material the electrons will move through and on the voltage.• More volts means more current

• Better conductors mean more current

• Current is a lot like the flow of water

• Measured in Amperes, sometimes called amps. (A)

• It is basically the amount of electrons that move through a spot in 1 second.

Current

So that is what is need to make current electricity…well almost. It isn’t good enough just to have electrons being pushed. They have to have somewhere to go.

• Electricity must have a complete circuit in order to flow.

• A circuit is a closed loop that allows for electrical current to flow.

Circuits

• Circuits have 3 basic parts

• Power Source – supplies the voltage

• Path – usually wires. Have electrons that can move

• Load – converts electrical energy into a useful energy

Circuits

Although a circuit can just be a power source and a path, there isn’t really a whole lot of point to that. Why not make that electricity do something?!

• Electricity is used by adding a load to a circuit. A load is a object that converts electrical energy into:• Light

• Heat

• Sound

• Motion

• Loads have a property called resistance.

• Resistance is how much the electric current (speed of electrons) has to push against• It is kind of like how much friction the electrons

experience

• Things that use electricity (like a light bulb) have higher resistance because they use electrical energy

Loads and Resistance

Circuit Diagrams• Circuits are really messy to look at in real

life

• Circuits are represented on paper with a circuit diagram

• It is a quick sketch that shows all of the part of a circuit

• Always has square corners and the different parts of the circuit are connected with a line

Circuit Diagrams

Circuit diagrams make electrical wiring easier to understand

They have a universal code of symbols so that no matter what language you speak, people can understand how the circuit is made

The Power Source• Each circuit must have a power source

• The power source provides voltage to the circuits• Without one, the electrons would have no push.

Without a push there is no current

• There are 2 main types of power sources:• DC – Direct Current – Electrons flow in 1 direction• AC – Alternating Current – Electrons flow both

directions

• Direct Current (DC) is where electrons flow in 1 direction in a circuit

• Electrons always flow from negative to positive

• DC power sources are things like batteries and solar panels

• They get the following symbols:

• Cells (batteries)

Short line is negative

Long line is positive

Direct Current

• DC Power Sources• Solar

panels

Alternating Current• Alternating Current (AC) is when

electrons flow both directions in a circuit

• It is impossible to know which direction electrons are moving at any time

• AC power is made by generators and is what come out of our outlets (plugs or sockets)

• AC Power Sources get the following symbol in circuit diagrams:

Draw arrows around the circuit to show which direction the electrons are moving in circuits

Examples

The Load

• The load in a circuit transforms electrical energy into a different type of energy

• We then use this energy for many different applications

Type of

Energy

Made

What Energy ‘Looks’

Like

Circuit Diagram Symbol

What Goes in Circuit

Light Energ

y Light Light Bulb

Heat Energ

yHeat or Warmth Resistor

Sound Energy

Sound or Noise Speaker

Mechanical Energy

Motion or Movemen

tMotor

Circuit Diagram Symbols You Must Know

Power Sources

Label these Power Sources

• Cell (batteries)

• Direct Current

• AC Power Source

LoadsLabel these Loads

Resistor

Speaker

Light

Motor

Other Important Symbols

Switch

Voltmeter

Ammeter

Connecting Wire

1) Draw a circuit with a DC power source and a light bulb

2) Draw a circuit with an AC power source, 1 resistor, and 1 motor

3) Draw a circuit with 2 batteries, 1 speaker, 1 light, and 1 resistor

Examples

Series and Parallel CircuitsThere are two types of circuits that can be made

• Series Circuit

• All of the objects in the circuit are connected one after another

• The electricity has only one path to take

Parallel CircuitThe electricity has more than one path to take in the circuit

Series Circuits

• The electricity has no options in a series circuit

• It must travel through 1 path

• In the example below, the electricity must go through every single light bulb before it gets back to the battery

• This example has 3 lights in series

Parallel Circuits• When a circuit is parallel the

electricity can take more than one path

• Electricity takes different paths at nodes

• In the example to the right, there are 3 lights, each in parallel

Say if the circuits below are in series or in parallel

Examples

1. Draw a circuit with an AC power source and a motor and light bulb in series

2. Draw a circuit with a DC power source and a speaker and resistor in parallel

3. Draw a circuit with 3 batteries, a light and motor in series, and a speaker parallel to the light.

Drawing Examples

Combination CircuitsCircuits can have a combination of both series and parallel

The circuit above has:-R3 parallel to R2

-R1 and R2 in series-R1 and R3 in series

What does the circuit above have?