This document outlines a unit on electrical science principles. It identifies three main sources of electromotive force: magnetic, chemical, and thermal. Magnetic force is generated by rotating a coil in a magnetic field, producing alternating current. Chemical sources include batteries and cells, where two dissimilar metals and an electrolyte produce direct current. Thermal sources use the Seebeck effect where applying heat to connected dissimilar metals produces voltage. Effects of electric current include heating, chemical changes through electrolysis, and generating magnetic fields around conductors.

1. 
202/1 – Know the principles of
electricity
Outcome 1.2/1.3 – Sources of
electromotive force & current
effects
Unit 202 Principles of electrical
science

2. 
1.1 Describe the reaction of electrons
when charged to form an electric
current
Last session

3. 
Unit 202 Principles of electrical
science
Unit 202 summative assessment
June 2015 (TBC)

4. 
1.2 Identify sources of an electromotive
force
MAGNETIC
CHEMICAL
THERMAL
1.3 Describe the effects of an electric
current
This session

5. 
Sources of an
electromotive force

6. 
A.C.
voltages

7. 
If coil of wire is rotated in a
magnetic field it will generate an
a.c. voltage
https://www.youtube.com/watch?
v=zOdboRYf1hM
a.c. generator

8. 
Components:-
Permanent magnet (stator)
Magnetic field
Coil of wire (armature)
Slip rings
a.c. generator

9. 
http://www.youtube.com/watch?feature=player_
detailpage&v=i-j-1j2gD28
A.C. Generator

10. 
D.C. battery

11. 
What is the difference?
Cell or battery?

12. 
What is the difference?
A cell is a single source.
A battery is a number of cells.
Cell or battery?

13. 
Although a single source is
actually a cell, it is
commonly known as a
battery
Cell or battery?

14. 
The first cell was made by
Alessandro Volta in 1799.
Copper and zinc disks
separated by a brine
soaked cloth.
The cell

15. A cell is very easy to make.
Two dissimilar metals in an alkaline or
acid solution.
4 cells as a battery

16. 
Copper is the anode.
Zinc is the cathode.
Dirt is the electrolyte
4 cells as a battery

17. 
Eventually, the electrolyte will lose it’s
chemical qualities and the battery will
be flat
4 cells as a battery

18. 
This type of cell cannot be re-charged
It is called a primary cell
The cell

19. A primary cells electrolyte can be either liquid or a paste.
Paste being more common and the type we would
recognise.
The primary cell

20. A secondary cell can be recharged once it is flat.
What are the most common types?
The secondary cell

21. A secondary cell can be recharged once it is flat.
What are the two types?
Lead-acid cell alkaline cell Lithium ion cell
The secondary cell

22. 
Lead-acid cell, typical example is a car battery.
Used to start a car, then recharged while car is running
The secondary cell

23. 
Looking inside

24. alkaline cell, rechargeable batteries.
Can be nickel-iron, nickel-cadmium, or lithium-ion.
The secondary cell

25. 
The secondary cell

26. 
 Build a potato cell
 Measure output voltage
 Connect all ‘potateries’
in series(anode to cathode)
 Calculate the output voltage
 Measure the output voltage
Potato battery

27. 
A D.C. generator does not have slip
rings, instead it has a commutator.
A commutator keeps the positive end
of the loop connected to one of the
output cables.
d.c. generator or dynamo

28. 
d.c. generator

29. 
Components:-
Permanent magnet (stator)
Magnetic field
Coil of wire (armature)
Commutator
d.c. generator

30. 
Heating - The heating effect of electric current is used in many everyday devices.
Electric cookers, kettles and toasters are among the household appliances that rely on it.
Joule’s Law states that the rate at which heat is produced in a resistor is proportional to
the square of the current flowing through it, if the resistance is constant
Chemical - Passing an electric current through a liquid causes chemical changes in a
process called electrolysis. Electroplating uses electrolysis to put a layer of one metal on
top of another. Examples include chromium plating of bathroom and car parts, and
silver plating of cutlery and jewellery.
Magnetic - Electric current passing through a wire generates a magnetic field around
the wire. This effect is used in all sorts of ways. Examples include electric motors and
electromagnets. In a car, for example, the central locking uses electromagnets called
solenoids to operate the lock mechanism. Another widespread example is the
loudspeaker, where variations in the magnetic effect of an electric current are
translated into sound waves that we can hear.
Describe the effects of an
electric current

31. 
REMEMBER - If a coil of cable is
rotated in a magnetic field
It will generate a voltage.
Magnetic effect
When an electric current passes
through a conductor a magnetic field
appears around it.
The magnetic field increases when the
wire is formed into a coil.
If the coil is wound on an iron core the
iron will become magnetised.

32. 
In 1821 Thomas Seebeck discovered a thermal
effect of electrical current.
If two dissimilar metals were connected together
at one end and heat was applied, a voltage
appeared at the cooler open end.
Thermal effect

33. 
As the difference in temperatures T1 and T2
increases, so does the voltage.
Through tests, a specific voltage will indicate a
specific temperature. This is called a?
The Seebeck effect

34. 
As the difference in temperatures T1 and T2
increases, so does the voltage.
Through tests, a specific voltage will indicate a
specific temperature. This is called a?
thermocouple
The Seebeck effect

35. 
Where could a thermocouple be used?
Thermocouple

36. 
Where could a thermocouple be used?
Ovens
Water heaters
Furnaces
hair straighteners
Thermocouple

37. 
Describe the chemical and thermal effects of electrical
currents.
 Two DISIMILAR metals and an electrolyte make a _______
 This is a _________ effect of electrical current.
 A secondary cell can be?
 Magnetic effect?
 Seebeck discovered a ____________ effect of electrical current.
This device is called a ________________.
 A difference in _____________ will create a voltage at the open end.
consolidation

38. 
1.2 Identify sources of an electromotive
force
MAGNETIC
CHEMICAL
THERMAL
1.3 Describe the effects of an electric
current
Consolidation

39. 
1.4 Identify SI Units for various
electrical quantities
Current, potential, resistance, resistivity,
temperature, mass, force, magnetic flux,
magnetic flux density, period, frequency,
power, energy, time, length, area, mass,
weight.
1.5 Transpose basic formulae.
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