Upload
julia-lewis
View
235
Download
0
Tags:
Embed Size (px)
Citation preview
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?