1. Electricity
Unit D

2. Introduction

3. Static Electricity
Section 1.1

4. Static Electricity
Imagine that you are hurrying down a hallway and you reach for a doorknob. Zap!
What just happened?
This is one type of electricity in action
Static electricity – static electricity is a stationary electric charge, usually caused by two objects having been rubbed together
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5. Static Electricity
The explanation for static electricity starts with the atom itself
Recall from Unit B that the atom is made up of a nucleus, which contains protons and neutrons, and electrons whizzing around the nucleus
Electrons are negatively charged particles, while protons are positively charged particles

6. Bill Nye https://www.youtube.com/watch?v=sd9SjA1B7R8 Furs and Rods
What do you notice about each rod when it was rubbed with the fur?
When they were brought close together?

7. Electrical Charge Think about what you saw in the video
What happened when two similar objects were brought close together?
How about two different objects?
Why do you think this is?
The objects reacted to each other in these ways because they were electrically charged
Most objects have equal amounts of positive and negative charge, which makes them neutral. However, sometimes there is more of one type of charged particle than another.

8. Electrical Charge
An object that has more electrons than protons is negatively charged (-).
An object that has more protons than electrons is positively charged (+).
The object then has a build up of static charge. 6 4
6 + (-4)

9. Electrical Charge
According to modern theory, static charges on solid materials are due to the movement of electrons from one object to another.
Franklin’s experiment of rubbing amber with fur helped establish laws that describe the behavior between charged and uncharged objects.

10. Laws of Electrical Charge
Unlike charges (opposites) attract
Like charges repel
Charged objects attract neutral objects

11. Charge Separation
Charge separation occurs when a charged object is brought close to a neutral object.
In the situation below
The (+) particles attract the (-) particles of the neutral object.
The area closest to the (+) object then has a (-) charge which attracts the (+) object.

12. Electrical Discharge
Electrical discharge: Occurs when a static charge (negative) is built up in an object.
The negative charge is attracted to the positive charge of another object (charge separation).
That attraction causes the electrons to jump to the other object.
Sometimes the static discharge is seen or felt as a spark.
Can you think of an example of this?

13. Lightning – Static Discharge
Occurs when strong winds and the collision of water droplets and ice particles in the clouds strip electrons from some particles and deposit them on others.
For reasons that meteorologists do not completely understand, negative charges collect at the bottom of the clouds while higher parts of the clouds are positively charged.
It is believed that this contact between different materials, followed by their wide separation, is what causes the cloud to be electrified.

14. Lightning – Static Discharge
The negatively charged bottom portion of the clouds repels electrons on the surface of the Earth, leaving the ground positively charged just below the cloud.
The strong attraction between the negative cloud and the positive ground pulls electrons off atoms and molecules in the air.
Once a chain of ions forms, the gigantic discharge (which we call lightning) occurs between the cloud and the ground.

16. Van der Graaf Generators
A Van der Graaf generator creates large amounts of static electricity by using friction
A rubber belt rubs on a piece of metal and transfers the charge to the sphere
The charge builds up on the sphere and transfers to you when you touch the sphere

17. Assignment
Check and Reflect Pg. 278
#1-4, 6-9

18. Homework Assignment
Protons are found in the nucleus of the atom, and they are positively charged. Electrons circle the nucleus, and are negatively charged.
“statically charged” means an object has an excess of a particular charge. For example, a balloon that has collected excess electrons is statically charged.
VDGs build up static charge by using friction. A source of charge is rubbed against a belt, and the belt transfers the charge to a sphere at the top of the VDG.
Like charges repel; unlike charge attract.
Sometimes we describe a neutral object as uncharged, meaning that there is no net charge. If we want to be more accurate, we may note that there are actually charges in a neutral object, but there are equal numbers of positive and negative.

19. Homework Assignment
A charged object will cause charge separation in a neutral object. For example, the negative charges in the neutral object will move away from an approaching negative object, leaving a positive area.
The plastic is neutral. When the negatively charged rod approaches, positive charges in the plastic are attracted to the negatively charged rod, so the plastic “jumps” to the rod. But once the plastic contacts the rod, electrons move into the plastic, giving it a net negative charge, so it is now repelled by the negative rod (like charges).
Large smooth trucks can acquire a large negative charge due to friction with the air. When these negative charges discharge, they can ignite flammable liquids, leading to dangerous fires and explosions. The metal wire touching the ground allows the electrons to continually discharge, so no dangerous static charge can build up.

20. Current Electricity
Section 1.2

21. Current Electricity
Static electricity is not useful for operating electrical devices, because they build up and then discharge
Electrical Current
The steady flow of charged particles is an electrical current
Current Electricity
Electricity that flows continuously
0-3:30

22. Electrical Current
Current electricity is the type that is used to power devices
Unlike static electricity, current electricity flows continuously as long as two conditions are met:
The flow of electrical current requires an energy source
There must a complete path or circuit for the charged particles to pass through
Demo
Electric Pickle

23. Electrical Current

24. Circuits A circuit is the path that controls the flow of electricity
If you compare electricity with water, this is like the water system in your house. The pipes and taps control the flow of water.
In most circuits, the path that electrons take is simply a conducting wire. However, some circuits can include gases, fluids, etc.
A conductor is anything that allows the flow of electrons

25. Circuits
Circuits generally include a conductor, an energy source and a load
A load is a device used to convert the electrical energy into another form of energy

26. Amperes
Imagine a fast-flowing river. If you were to describe the current you might state the number of liters of water that flow past a certain point every minute.
Similarly, scientists describe electric current as the amount of charge that passes a point in a conducting wire in a given time.
The symbol for current is I.
The rate at which an electrical current flows is measured in amperes (A)
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27. Electrical Energy and Voltage
Electrical energy is the energy carried by charged particles
Voltage is a measure of how much electrical energy each charged particle carries
The higher the voltage, the greater the potential energy of each particle
The unit of voltage is the volt (V), names for Alessandro Volta

28. Measuring Voltage
The simplest way to measure voltage is by using a voltmeter
Demo – using a voltmeter

29. Assignment
Check and Reflect Pg. 283
#1-6, 8

30. Homework Assignment
Electrical energy is the energy carried by charged particles.
Current electricity flows continuously, while static electricity is built-up negative charge that can be discharged.
Voltage is how much electrical energy each particle carries. It is often referred to as potential difference, because it is responsible for providing potential energy to electrons that allows them to flow.
a) current is measured in amps (A); b) voltage is measured in volts (V)
If you need a high-current battery, you should pay particular attention to the number of amps a battery can deliver – the higher the amps, the higher the current.

31. Homework Assignment
This statement may be accurate if the current is travelling at the same rate in both wires, with the same voltage. However, a wire with fewer electrons can deliver more energy if the electrons are travelling faster (higher current) and carry more energy per particle (higher voltage).
Electricity is the flow of electrons not a quantity of electrons. Without being connected to a source of voltage, the electricity cannot flow in the hairdryer, no matter how many electrons it contains. You need a complete circuit in order to make the appliance work.

32. Electrical Safety
Section 1.3

34. Electrical Safety Do! Don’t! Stay away from power lines.
Call the Power Company to retrieve model airplanes and kites caught in a tree near power lines.
Use appliances only as designed and directed by the manufacturer.
Replace frayed cords.
Report downed trees that are near or on fallen power lines.
Get indoors or in a car during an electrical storm.
Turn off appliances when not in use.
Unplug computers and televisions during electrical storms.
Don’t fly a kite near power lines.
Don’t climb a tree, ladder, or pole near a power line.
Don’t climb the fence of a substation.
Don’t use a metal knife or fork to lift toast out of the toaster unless the toaster is unplugged.
Don’t use an appliance with a frayed cord.
Don’t use golf clubs or shoes with metal cleats during an electrical storm.
Don’t paint or wall paper over wall switch covers or outlets.
Don’t run cords under carpets.
Don’t use a telephone during electrical storms.

35. Electrical Safety Electricity is always trying to get to the ground.
Like all good travelers, electricity takes the shortest and easiest route whenever it can.
If something that conducts electricity gives electricity an easy path to the ground, electricity will take it!

36. Electrical Safety http://www.youtube.com/watch?v=l-wXyw0tvSA
Water and metal are some of the best conductors for electricity.
Because your body is mostly water, you are a great conductor.
So if you touch a conductor and the ground at the same time, you will become electricity’s easiest path.

37. Electrical Safety
Electricity will flow through you, and you could be seriously hurt or even killed.
You don’t have to be touching the ground directly to conduct electricity.
You could also be touching something that is in contact with the ground, like a tree or a ladder.

38. Electrical Safety Water is an excellent conductor.
You can become electricity’s path to the ground if you are touching water that touches electricity.
Electricity would travel through the water and through you to the ground.

39. Electrical Safety
This is why it’s so important to keep all electrical appliances away from water, and to make sure your hands are dry and you are not standing in water when you touch anything electrical.
It’s also the reason no one should ever use water on an electrical fire, but should use a multipurpose fire extinguisher instead.

40. Electrical Safety
Appliances have protective insulated cords and coverings to keep you from contacting the electricity inside.
It’s important to use appliances and cords the way they were designed to be used so you don’t damage the insulation or contact live electrical parts.
If a live wire inside an appliance, toy, or power tool touches the inside of the device and you touch the device, it would be like touching a bare live wire.

41. Electrical Safety
You cannot tell from the outside of there is a problem inside, so you should always act as if there were danger of shock.
You can never tell when contact with electricity will be fatal, but you can be sure it will always hurt.
Electric shock can cause a loss of muscle control, weakness, rapid pulse, severe burns, unconsciousness, or death.

42. Electrical Safety
In a shock incident, the path that electric current takes through the body gets very hot.
Burns occur all along that path, including the places on the skin where the current enters and exits the body.
It’s not only giant power lines that can kill or injure you if you contact them.
You can also be killed by a shock from an appliance or power cord in your home

46. I wonder...
Have you ever wondered why the birds that sit on power lines don’t get electric shocks?
It’s because the electricity is always looking for a way to get to the ground, but the birds are not touching the ground or anything in contact with the ground.

48. Amps vs. Volts Which one is more dangerous?
The number of amps is much more important than voltage when assessing the potential danger of an electrical shock
If A passes through your body you probably wouldn’t feel it
0.015 A – A will cause you to lose muscle control and a painful shock
Current as low as 0.1 A can be fatal

49. Assignment
Check and Reflect Pg. 287
#1-10

50. Homework Assignment
Both are dangerous. When someone is shocked it is the amount of current that causes the damage, and even small currents can kill. High voltage is dangerous because it drives the current. The most dangerous shock is from a current at high voltage.
A fuse will melt when too much current is flowing through the circuit. This interrupts the current flow and protects the circuit.
Ground wires conduct electrical discharges harmlessly to Earth, instead of having them flow through circuits and harming them.
A short circuit is an unintended path for current, which bypasses the normal circuit.
The rubber tires of a car are insulators, preventing electricity from flowing through the car into the ground. Therefore, there is no complete circuit and no flowing current, so the people inside are not electrocuted.
Not all shocks are dangerous. Most people encounter harmless electrostatic discharges everyday.

51. Homework Assignment
Lightning rods are the tallest point on the building, therefore they are more likely to be subject to a lightning strike. Lightning rods conduct electrical discharges harmlessly to the ground, protecting the building.
Bathwater is a conductor. If the radio were to tip into the water, current would flow through the water and through the person taking the bath, and could be fatal.
Lightning tends to strike high points like trees, and the tree will be a good conductor – you are likely to receive some of the current if the tree is struck.
Removing the third prong is a bad idea. This prong connects the device to the ground, proving a route for dangerous current to flow in the event of a short circuit in the device. If the prong is removed, it is more likely a short circuit could result in someone being electrocuted.

52. Cells and Batteries
Section 1.4

53. Cells and Batteries
Luigi Galvani ( ), who noticed that a frog’s muscle would twitch when touched by two different metals, could hardly have imagined the outcome of his observations.

54. Cells and Batteries
Galvani believed that the frog’s tissue had a unique ability to generate “animal electricity”.
Later, Alessandro Volta showed that a voltage could be generated without using living tissue by placing different metals in a solution containing a conductor or electrolyte.
Today, such a device is called an electrochemical cell.
In any electrochemical cell, two different metal conductors are surrounded by an electrolyte, a substance that can conduct electricity because it contains chemicals that form ions.

55. Dry Cells
A dry cell is a cell which contains chemicals in the form of a paste
The chemicals undergo a chemical reaction to release free electrons from the negative terminal which pass through the device using the cell as a power source before returning to the positive terminal of the cell
They have the advantage of not leaking (can be used in any position) because they are sealed

56. Dry Cells
An electrolyte is found in the cell which conducts electricity because it can form ions
The electrolyte paste reacts with the two metals, called electrodes
As a result of this reaction, one end becomes positively charged while the other end becomes negatively charged

57. Wet Cells Wet cells use a liquid electrolyte.
The reaction remains the same
Electrons are released from one electrode and travel through a wire to another electrode, creating an electric current
Car batteries contain several wet cells.

59. Cells and Batteries
The chemical reaction in a cell determine the potential difference (voltage) that the cell can create.
Very few single cells can produce more than 2 V.
To obtain higher voltages, batteries contain several cells connected in a row.

60. Rechargeable Cells
If a cell cannot be recharged (a primary cell), the amount of chemicals it contains determines the total amount of electric energy the cell can produce.
Rechargeable secondary cells use chemical reactions that can be reversed.
In a re-charger, electricity is forced through the “dead” cell, rebuilding the original chemicals allowing the cell to be reused.

61. Electrochemistry
Electrochemistry – The study of chemical reactions involving electricity.
Electrolysis – The process of using batteries to split molecules into their elements.
The electrolysis of water splits the molecules into pure hydrogen and pure oxygen.

62. Electroplating
The deposition of a metallic coating onto an object by putting a negative charge onto the object and immersing it into a solution which contains a salt of the metal to be deposited.
The metallic ions of the salt carry a positive charge and are attracted to the negative.
When they reach it, the negatively charged part provides the electrons to reduce the positively charged ions to metallic form.

63. Electroplating
Electroplating is used to coat cheaper metal with silver or gold to create jewelry and other products which look good, but are less expensive than pure gold or silver

65. Assignment
Check and Reflect Pg. 294
#1-8, 10

66. Homework Assignment
Electrolysis is the splitting of molecules into their elements with the use of electricity.
An electrolyte is a paste or liquid that conducts electricity because it contains chemicals that form ions.
Alessandro Volta made the first practical battery by piling copper and zinc discs alternately in an electrolyte.
The chemical reactions in a rechargeable cell can be reversed with the application of an external electric source.
A wet cell would be more practical. They are cheaper, last a long time, and are rechargeable.
Draw on board.

67. Homework Assignment
Dry cells contain chemicals that react to produce a potential difference. When the supply of reactants runs out, it can no longer provide energy for a circuit.
Draw on board.
If the electrodes were made of the same substance, they cannot become differently charged when exposed to an electrolyte. Therefore, the cells with electrodes of the same substances would not work (a, c and e). The others would work (b and d).