1. How Do Charges Flow Through the Components of a Circuit?
Topic 3.3

2. Review
1. What will happen if a positively charged object gets close to another positively charged object?
2. What will happen if a positively charged object gets close to a negatively charged object?
3. Using + and -, draw a positively charged object, a negatively charged object and a neutral object
Question for today:
How do you think a battery works?

3. Review
1. What will happen if a positively charged object gets close to another positively charged object?
They will repel!
2. What will happen if a positively charged object gets close to a negatively charged object?
They will attract!
3. Using + and -, draw a positively charged object, a negatively charged object and a neutral object
Question for today:
How do you think a battery works?

4. 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.

6. Concept 1: Chemical Energy Separates Electrical Charges In Cells
Transforms energy into energy
Example: an AA “battery” is an electrochemical cell, even though it is commonly known as a “battery”)
Electrochemical cell:
chemical
electrical

7. Electrodes
In a cell, chemical reactions of two different or compounds occur on the surface of
an electrode is a conductor through which an object, substance, or region
Electrodes in solutions are called
metals
metal
electrodes
electricity
enters or leaves
electrolytes

8. How Electrochemical Cells Work
The reactions cause one electrode to
become charged and the
other becomes charged
The electrodes are in contact with the
in the cell
When terminals are connected to an
electrical pathway, charges flow through it
positively
negatively
terminals

9. Two Types of Electrochemical Cells
Both types transform chemical energy into electrical energy
- contains a
as an electrolyte
Dry cell
moist
paste
Figure 3.13: A dry cell (electrolyte is a paste)

10. Two Types of Electrochemical Cells
- the electrodes sit in a
Wet cell
liquid
solution
Figure 3.13: A wet cell

11. Battery two or more cells sources Battery – a connection of
E.g. you make a battery when you put AA cells together in an electrical device
Often, several electrochemical cells can be packaged together to make a battery
Electrochemical cells and batteries are (anything that supplies electrical energy)
two or more cells
Electrical outlets are also sources
Figure 3.14: The battery shown here is made up of six individual electrochemical cells.
sources

12. Understanding How an Electrochemical Cells Works
Chemical energy separates the positive and negative charges
Energy is the
Work is done on an object when a acts on it and moves it some
Electrons now have energy to do other work
Electrical energy now stored in the cell is a form of (it has the potential to do work)
ability to do work
force
distance
Because opposite charges attract each other, it takes energy to separate the positive and negative charges.
From the last topic, friction can provide this energy
Chemical energy from chemical reactions does the work of separating the charges.
Energy is the ability to do work. Work is done on an object when a force acts on it and moves it over a certain distance.
Because work went into separating the charges, the electrons now have energy to do other work, e.g. running a fan
It has the potential to do work because of the separation or position of the charges
potential
energy

13. Understanding How an Electrochemical Cells Works
The worker (chemical energy) carries (electrons) up a ladder and places them at the
The worker leaves on the bottom of the
Only a small amount of electrical energy is stored in the cell
negative charges
negative terminal
positive charges
The first electron is easy to carry up, since only one pair of charges is being separated and the attraction is not very strong
positive terminal
Figure 3.15: The worker represents chemical energy

14. Understanding How an Electrochemical Cells Works
After a few charges have been separated, the attraction between the charges at the terminal and the charge of the electron being carried
The negative charges of the electrons at the negative terminal are the negative charge of the electron being carried
Therefore, it takes more energy to carry each additional electron
The worker (chemical energy) has done a lot of work to separate the charges
This energy is stored in the of the separated charges
positive
positive
negative
increases
repelling
All of the positive charges of the positively charges ions are attracting to the negative charge of the electron that the worker is carrying.
At the same time the negative charges of the electrons at the negative terminal are repelling the negative charge of the electron
So it takes more energy each time to carry the electron up the ladder
The worker (chemical energy) has to done a lot of work to separate the charges. This energy is now stored in the electrical potential energy of the separated charges
Figure 3.15: The worker represents chemical energy
electrical potential
energy

15. Understanding How an Electrochemical Cells Works
Eventually, repulsion of the electron by the negative charges at the negative terminal and the attraction by the positive charges gets so strong that the worker cannot carry any more electrons
No more chemical energy will be transformed into electrical potential energy
The battery is now
Complete handout
Figure 3.15: The worker represents chemical energy
charged

16. Classifying Cells Cells are either or
Another classification depends on whether they can be
Primary cell – can be use , then discarded
Secondary cell – can be recharged
To recharge a secondary cell, an electric current is passed in the direction through the cell from a source
The charging current reverses the chemical reactions in the cell, restoring the cell to full capacity
dry
wet
recharged
only once
many times
opposite

17. Electrical Potential Difference
A unit of charge is called a
When a unit of charge passes through a , it
The quantity used to measure this is called
Often call this
Symbol: V
Units: volts (V)
coulomb
source
gains
electrical potential energy
electrical
A coulomb gains electrical potential energy when it passes through a source (such as a battery)
Because of the symbol and units, electrical potential difference is often called voltage
For this reason voltage is used on cells and batteries
potential difference
voltage
Figure 3.16: A typical AA or AAA cell provides an electrical potential difference (voltage) of 1.5V.

18. Electrical Potential Difference
It measures the difference in electrical potential energy per unit of charge between the positive terminal and the negative terminal in an electrochemical cell
The electrical potential difference is often called the voltage
1.5V cell: it took 1.5 units of energy to
separate the last unit of charge
(i.e. carry the last unit of charge “up the
ladder”
Why is electrical potential difference called a difference?
Think of it this way: to charge a cell, a chemical reaction does work to separate electrons and positive ion. It takes more energy to carry each electron up the ladder.
This is because the forces of attraction and repulsion acting on it get stronger and stronger
Separating the final charges requires the most energy of all
The electrical potential difference of the cell represents the amount of energy it took to carry the last unit of charge up the ladder
The electrical potential difference of a cell is determined by the nature of the chemical reaction that happens in the cell
Cells and batteries are rated according to their electrical potential difference between one terminal and the other
Other sources, like electrical outlets, are rated in a similar manner
If two cells are linked together, their voltages add up
E.g V cells placed together in a radio = their voltage or electrical potential difference is 3V
Figure 3.16: A typical AA or AAA cell provides an electrical potential difference (voltage) of 1.5V.

19. Discussion Questions
Use an analogy other than a worker and a ladder to explain how chemical energy is transformed into electrical energy in a cell.
Why is the electrical potential difference of a source referred to as a difference?
Do video before discussion questions