1. Unit 10 - Electricity

2. What is electricity?
Electricity – form of energy caused by moving electrons

3. The Atom
the atom has three basic parts
Proton
Neutron
Electron

4. The Atom the protons and neutrons are found in the nucleus
the electrons are found in a cloud around the nucleus

5. The Atom Protons have a positive (+) charge
Electrons have a negative (-) charge
Neutrons are neutral

6. The Atom
objects with the same charge repel, or move away from, each other
objects with different charges attract each other
most objects are electrically neutral

7. The Atom Electrons can move from place to place
Electrons always move from a negatively charged area to a positively charged area
this movement of electrons is the basis of electricity

8. Insulators & Conductors
Conductors – materials that allow electric charges to flow through them easily

9. Insulators & Conductors
some conductors are better than others
most metals are good conductors of electricity

10. Insulators & Conductors
Insulators – materials that prevent electric charges from flowing through them easily

11. Insulators & Conductors
some examples of insulators include:
rubber
cork
wood
plastic

12. Insulators & Conductors
electric wires use both insulators and conductors
a conductor, often a copper wire, is coated with an insulator, such as rubber
if the insulator wears out and the wires come in contact, a short circuit occurs, allowing the electricity to jump between the wires

13. Electric Current
electric current – flow of electrons through a conductor
the number of electrons flowing determines the amount of electric current
there are two types of electric current:
Direct Current
Alternating Current

14. Electric Current
direct current – current in which electrons always flow in the same direction
current always flows from the negative pole to the positive pole
all batteries provide direct current

15. Electric Current
alternating current – current in which electrons change direction at a regular rate
most electricity that is used in everyday life comes from alternating current

16. Electric Current
alternating current produces less heat, when carried by wires from power plants, then direct current
this results in less damage to power cables

17. Batteries battery – series of electrochemical cells connected together
electrochemical cell – device that changes chemical energy into electrical energy
a battery is a source of direct current

18. Batteries
when you connect the negative and positive poles of a battery to a conductor, electric current flows through the conductor

19. Batteries
there are two types of batteries:
wet cells
dry cells

20. Batteries
the simplest type of electrochemical cell is called a wet cell
a wet cell has three parts:
negative pole
positive pole
electrolyte

21. Batteries
electrode – positive or negative pole of an electrochemical cell
the negative electrode is often made of zinc
the positive electrode is often made of copper

22. Batteries
electrolyte – substance that dissolves in water to form a conducting solution
sulfuric acid is often used as an electrolyte

23. Batteries
a chemical reaction in the wet cell causes electrons to build up on the zinc electrode
when the two electrodes are connected by wire, electrons flow from the zinc to the copper electrode

24. Batteries
the most familiar type of electrochemical cell is called a dry cell
a dry cell works the same way as a wet cell with a positive electrode, a negative electrode, and an electrolyte

25. Batteries the electrolyte is a moist paste inside the cell
the negative electrode is the outside case of the battery which is usually made of zinc
the positive electrode is located inside the battery and is sometimes made of carbon

26. Batteries
newer style dry cell batteries use nickel oxide for a positive electrode and cadmium for a negative electrode
these are called nickel-cadmium, or ni-cad, batteries

27. Electric Circuits
electric circuit – path that an electric current follows
all electric circuits have three parts
source of electric current
load (something that uses electricity)
wires (connect the source to the load)
most electric circuits also have a switch

28. Electric Circuits there are two types of electric circuits
series circuit
parallel circuit

29. Electric Circuits
series circuit – circuit in which electric current follows only one path
a series circuit is the simplest type of electric circuit

30. Electric Circuits
parallel circuit – circuit in which electrical current can follow more than one path
if several appliances are connected in a parallel circuit, current can still reach the other appliances if one of them stops working
parallel circuits are used in homes, schools, and office buildings

31. Volts, Amps, & Ohms
electromotive force – force that makes electrons move
electromotive force is abbreviated EMF

32. Volts, Amps, & Ohms volt – unit used to measure electromotive force
voltage is measured with a voltmeter

33. Volts, Amps, & Ohms ampere – unit used to measure electric current
one ampere, or amp, is the amount of current passing a point each second

34. Volts, Amps, & Ohms
the amount of electric current depends on the number of electrons flowing in a circuit
current is measured with an ammeter

35. Volts, Amps, & Ohms
as current flows through a wire, it meets resistance from the wire

36. Volts, Amps, & Ohms
resistance – opposition to the flow of electric current
Ohm – unit used to measure resistance

37. Volts, Amps, & Ohms resistance of a wire depends on: length thickness
material
temperature

38. Volts, Amps, & Ohms
length – the longer a wire is, the more resistance it has
width – the thinner a wire is, the more resistance it has
material – wires made of poor conductors have more resistance than wires made of good conductors
temperature – as a wire gets hotter, its resistance increases

39. Volts, Amps, & Ohms every closed circuit has: current (I) voltage (V)
resistance (R)

40. Volts, Amps, & Ohms
different power sources have different amounts of voltage
the resistance varies depending on the type of wires used
the current is affected by the voltage and the resistance

41. Ohm’s Law
Ohm’s law – current in a wire is equal to the voltage divided by the resistance
current = voltage / resistance
I = V/R

42. Ohm’s Law

43. Electric Safety
too much current in a circuit can cause an overloaded circuit
electric current comes into a house from power lines to a breaker box

44. Electric Safety
breaker boxes contain:
fuses or
circuit breakers

45. Electric Safety
fuse – wire that melts and breaks a circuit if too much current is flowing
by melting, the fuse stops current from flowing and prevents an overloaded circuit
fuses need to be replaced when they become overloaded
fuses are used in many older homes

46. Electric Safety
circuit breaker – switch that opens a circuit if too much current is flowing
a circuit breaker can be reset when it becomes overloaded
most newer homes have circuit breakers