1. Topic 3.3: Key Concepts
Chemical Energy separates electrical charges in cells.
Charges can flow through conductors, but not insulators.
Moving electrical charges form an electric current.
A load resists the flow of current.
Conductors must form a closed loop to allow current to flow.

2. Concept 2: Charges Can Flow Through Conductors, but Not Insulators
When 2 different solid materials are rubbed together, electrons can be transferred from one material to the other.
The electrons will either on the surface of the new material or
Any material that electrical charges can move through is called a
How easily charges move through a material is called
A material through which charges cannot travel is an
stay
Electrons can move through pretty much all metals, but some metals are better conductors than others
travel through it
conductor
conductivity
insulator

3. Discussion Questions
Explain why electrical wires are covered by an insulator.

4. Concept 3: Moving Electrical Charges Form An Electrical Current
from a source causes charges to move through the , carrying energy to the device
The moving charges are called an
Symbol for current:
Current is measured in :
Chemical Energy
conductor
electric current I
amperes A

5. Concept 3: Moving Electrical Charges Form An Electrical Current
For example, the equation I = 3 A means that the current (I), is three amperes (3 A)
A smaller unit of electric current is the milliampere
(1A = 1000 mA)
Discussion Question: Describe the relationship between moving charges and electric current.

6. Concept 4: A Load Resists The Flow of Current
- a device that converts electrical energy into another form of energy
E.g. A light bulb is a load that transforms electrical energy into light energy
As pass through a load, they energy as electrical energy is converted to another type of energy
Load
E.g. a radio is a load that transforms electrical energy into sound energy
electrons
Figure 3.18: A light bulb is a load because it converts electrical energy into heat and light energy.
lose

7. A Load Resists The Flow of Current
A load the flow of
Electrons in the current with atoms that make up the load, or with each other
The interfere with the flow of current
How much the flow of current in hindered is known as (symbol: )
unit of measurement is
resists
current
collide
E.g. a radio is a load that transforms electrical energy into sound energy
In general, metals have less resistance than non-metals, hence why they are better conductors.
collisions
resistance R
Ω (Ohm)

8. Factors Affecting Electron Flow
- the longer the wire, the the resistance because there is a higher chance that the electrons will collide with other ions and electrons along the way.
Length of conductor
higher

9. Factors Affecting Electron Flow
- the thicker the wire, the the resistance because there are many more atoms, and more free electrons in the wire to carry the current
Thin wires have resistance because there is for the electrons to move
- the the temperature, the higher the resistance because increased movement of the atoms and ions creates more collisions with the moving electrons
Diameter
lower
less space
higher
Temperature
higher

10. Example of Resistance: Filament in a Light Bulb
Charges move from a large wire (electrical cord) into a thin wire (filament)
Since charges have less room in the filament (the filament the movement of charges), they collide with atoms so hard that the filament gets very hot
The heat makes the filament
glow (“light up”)
resists
Load has resistance – Video:

11. Discussion Questions
Use the source, current, and load to describe how you think a flashlight works

12. Concept 5: Conductors Must Form a Closed Loop to Allow Current to Flow
- made up of a , , and a connected in a way that allows current to flow
For current to flow, the circuit must form a
Example:
Source =
Load =
Conductor =
Electrical circuit
source
load
conductor
closed loop
Electrochemical cell
lightbulb
Wires

13. Short Circuits
Short Circuit – a circuit with a that is , making the current so that it is dangerous
Example: if there was not a load (light
bulb) to resist the flow of current, the
current would be so large that the
conductor would get very hot and
start a fire!
resistance
too
high
low

14. Modelling the Flow of Current (Part A)
Negative terminal repels the negative charges already in the conductor
Positive terminal attracts the
charges
already in the conductor
Electrons move along the
wires and electrons from the cell
move into the conductor
The conductors already have electrons in them
negative

15. Modelling the Flow of Current (Part B)
As the electrons pass through the , they transfer some of their energy to the load
The electrons then leave the
load and return to the
electrochemical cell
load
The conductors already have electrons in them

16. Modelling the Flow of Current (Part C)
Electrons enter the cell and combine with positive ions to become
Over time, there are fewer
electrons at the negative
terminal and fewer positive
ions at the positive terminal
The worker can carry more
electrons up the ladder, keeping
the number of separated charges
neutral
The conductors already have electrons in them
equal at all times

17. Controlling the Flow of Current
In a typical circuit, a controls in a circuit
Example:
switch is , meaning the circuit is , current from flowing
Switch is , meaning the circuit is , allowing current to flow through and the light turns on
switch
current
open
open
stopping
closed
closed
Figure 3.20: How a switch controls current in a circuit

18. Using Circuit Diagrams
Draw a circuit diagram from the previous slide’s image.

19. Example of a Circuit Diagram
Draw the circuit for the following image:
Draw a circuit diagram from the previous slide’s image.

20. Comparing Water & Electrical Circuits
Water circuit – a lifts the water to a higher level against the pull of
Electrical circuit – cell or battery is like the pump
pump
A valve at the top of the pipe controls where the water flows down. When the water runs down, it turns a water wheel
Electrical circuit – it raises charges to a higher level of electrical potential energy
The switch is like the valve. It determines whether the electrons are allowed to flow through the circuit. When the electrons are allowed to flow, the current runs through the load and lights the light bulb
gravity

21. Discussion Questions Explain what “short circuit” means.
Describe the role of a switch in an electrical circuit