1. Electrical Principles & Technologies
Science 9 Unit D Section 1.0
Electrical Principles & Technologies

2. 1.1 – Static Electricity
Static electricity is produced when two objects rub together
This produces a buildup of charge on the objects being rubbed together
How Static Electricity works

3. Protons have a POSITIVE CHARGE Electrons have a NEGATIVE CHARGE
The Atom
Protons have a
POSITIVE CHARGE
Electrons have a
NEGATIVE CHARGE

4. Electrical Charge
Positive and negative charges on an object are due to the ratio of protons and electrons present in an object
Objects are negative when they have more electrons than protons
Objects are positive when they have more protons than electrons
Objects are neutral when the amounts of positive and negative charges are equal

5. Producing a Charge
Charges are produced when electrons move from one object to another
An object that loses electrons becomes positively charged while one that gains electrons becomes negative
Only the electrons move, never the protons!

6. Charge Separation
Charged objects cause charge separation when they are brought near to neutral objects

7. Electrical Discharge
Static electricity generally does not move – it remains stationary (or is static)
However, a built-up static charge on an object can be attracted to other objects and jump to the object
Often this creates a small spark, which is known as an electrical discharge

9. Laws of Electrical Charges
Opposite charges attract each other
Like charges repel each other
Neutral objects are attracted to charged objects

11. Van de Graaff Generators
A Van de Graaff Generator is used to study electrical charges
A rubber belt running in the generator rubs against metal “brushes” and creates a static charge
The charge is then transferred to the metal sphere, where the static charge builds up

12. Mythbusters Van de Graaff generator

13. 1.2 – Current Electricity
Static charges do not work very well for operating electrical devices
Electrical current is produced as charges move in a continuous flow
An electrical current flows until it is used up or disconnected
Think of it like water flowing until it is dammed or its source drives up

14. Electric Eels http://www.youtube.com/watch?v=a3sviTa8hZw
World’s deadliest: Six-Foot Electric Eel

15. Amperes The rate at which current flows is measured in amperes (A)
Called Amp for short
Named after Andre-Marie Ampere
Electrical current refers to the number of electrons passing a point in a circuit per second

16. How do we move electricity to its destination?
Answer: CONDUCTORS
Conductors are materials that electrical energy can move easily through

17. Circuits A circuit is a path that controls the flow of electricity
(just like pipes and taps in a water system control the flow of water)
In most pathways, electricity flow along solid metal wires, but circuits can also include gases, other fluids, etc

19. Parts of a Circuit A complete electrical circuit consists of:
LOAD: a device that converts electrical energy to another form (ex. A lightbulb)
ENERGY SOURCE: source of electrical energy (ex. Battery)
CONDUCTOR: pathway for electricity to flow (ex. Wires)

20. Electrical Energy & Voltage
Voltage is the measure of the amount of electrical energy carried by each particle
Voltage is also known as “potential difference”
The unit for voltage is known as the Volt (V)
Voltmeters are used to measure voltage

21. Measuring Voltage
When setting up a voltmeter, the red lead must run to the positive battery terminal, and the black lead should run to the negative terminal

22. 1.3 Electrical Safety
Electricity has the ability to seriously injure or kill
This is because electrical current can interrupt the function of the nervous system and heart (both of which rely on their own electrical current to operate)

23. Short Circuit A short circuit is an unintended pathway for electricity
The current bypasses part of the normal circuit

24. Electrical Shock
High voltage is more likely to cause damage than low voltage
However, the number of amps is much more significant
This is because you may only have a few high-energy electrons flowing through you if there is a high voltage and a low current
However, high currents mean that lots of electrons are flowing through your body

25. Current Effects
0.001 A: Effects are likely not felt A: Painful shock and loss of muscle control A: Fatal

26. Protecting From Shock
Insulators prevent the movement of electrical current and will protect you from electrical shock
Current does not move freely through insulators such as wool, rubber, and air.

27. Electrical Safety Pointers

28. Plugs, Fuses & Breakers
The third prong on electrical plugs is the ground
This provides a route through which excess charge can escape to the ground (instead of building up and discharging through you!)

29. Plugs, Fuses & Breakers
Both fuses and circuit breakers limit the amount of current flowing through a circuit
If a fuse or breaker receives too much current, the circuit is broken and the current stops

30. Lightning The current in a lightning strike can be as high as 30 000 A
To avoid being hit by lightning, avoid the following:
standing on hilltops or under trees
standing near metal objects

31. Lightning Rods Lightning rods are often added to tall building peaks
They are connected to the ground with wires
Any discharge from a lightning strike is conducted harmlessly to the ground (instead of destroying the building or its wiring)

32. 1.4 – Cells and Batteries
An electrochemical cell is a device that provides a steady current that is produced by a chemical reaction
Some people have problems with the electrical signal that controls beating of the heart, a PACEMAKER can be surgically inserted to send small amounts of current to keep the heart beating normally
Electrochemical cells come in two types:
Wet cells and dry cells

33. Dry Cells
A dry cell is an electrochemical cell that uses chemicals in a paste form
The cell consists of two different metals and an electrolyte
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34. Dry Cells - Terms
An Electrolyte is a paste or liquid that conducts electricity
An Ion is an atom or group of atoms that has come electrically charge through the loss or gain of electrons
An Electrode is a metal that the electrolyte reacts with

35. Wet Cells A wet cell uses an aqueous solution as the electrolyte
Wet cells are less common than dry cells
Why?
They are more expensive, not as reliable and can leak

36. Chemical Reactions & Electrochemical Cells
In a wet or dry cell, the electrolyte reacts with the two metals
One metal loses electrons and becomes positively charged
The electrons are passed through the solution and are deposited on the other metal, which becomes negatively charged
When connected to a circuit, the electrons leave the negative electrode and move through the circuit to the positive electrode

37. Rechargeable Cells
Some dry and wet cells are primary cells (they cannot be recharged)
Secondary cells (which are rechargeable) can regain stored charge if an electrical current is run “backwards” through the cell
These cells use chemical reactions that can be relatively easily reversed

38. Batteries A battery is a collection of cells connected together
“AA”, “AAA”, “C” and “D” type cells are not batteries – they are single electrochemical cells
Larger batteries such as 9-V and 12-V batteries are true batteries

39. Volta Made the first practical battery
He piled many copper and zinc discs on top of each other, separating them with electrolyte-soaked paper discs

40. Electrolysis
Electrolysis is a technique that is used to break free atoms from compounds
This is done by running a current through the substance
For instance, electrolysis can be used to produce oxygen and hydrogen from water
Or separate pure metals from molten compounds

41. Electrochemistry
Is the study of chemical reactions involving electricity

42. Electroplating

43. Electroplating
A thin layer of metal can be plated onto a cheaper metal using electricity
The item to be plated is immersed in an electrolyte along with an electrode that consists of the metal that will be used for plating
Electricity flows from the plating metal to the object being plated, and as a result the metal moves across the solution and builds up on the surface of the object being plated

44. Other Applications of Electrochemistry
Anodizing – aluminum is coated with a layer of aluminum oxide, which is much harder than regular aluminum
Electrorefining – impurities are removed from impure metals by placing the metal in an acid and running a current through it