Chapter 21

1. Chapter 21 ELECTRIC CHARGE Front Load Notes all new Science Words

2. Front Loaded Words • First bullet is the definition. • Second and third bullets or following slides are key points or details & characteristics. • Includes similarities, differences.

3. Electric Charge 21-1 • pp. 592-597

4. STATIC ELECTRICITY: • The accumulation of electrical charges on an object. • The charge does not move! • Static means “not moving” or stationary

6. Electric Charge • Unlike charges produce an "attractive force" which pulls matter together. Like charges pushes away.

7. CHARGES (that attract, or pull ) • Unlike charges attract ( pull ) each other. • POSITIVE NEGATIVE

8. CHARGES(that repel, or push)

9. Becoming Charged • Electrons are gained or lost on object’s surface. • If electrons are gained = negative charge. • If lost = positive charge. • only electrons move from one object to another. Ex. Balloons, clothes in dryer.

10. Electric Field • Region around a charged object where the electric force is felt by other objects. • Shown by “Lines of Force”

11. Charging by INDUCTI0N: • The rearrangement of electrons on a neutral object caused by a nearby charged object. Ex. Balloon sticking to wall or wood cabinet.

12. Charging by CONDUCTION: • Charging by direct contact. • Original object is charged by rubbing. • Scrapes electrons off one object onto another object. Ex. Rubbing socks on carpet.

13. Conductors • Materials that allow electrons to move through them easily. • Electrical conductors, not heat conductors. Ex. Name some electrical conductors.

14. Electric Ground • Object connected to the earth so that a large static charge doesn't build up and cause damage when discharged. • Connected by a conductor. • Ex. Lightning rods and plumbing pipes.

16. Insulators • Material that does not allow electrons to move through it. • Electrical insulators, not heat. Ex. Name some.

17. Electroscope • Made of two thin metal strips called leaves to hanging from a metal rod attached to a metal sphere or plate.

18. Lightning 21-2 • pp. 598-599

19. Lightning • Lightning is a large discharge of static electricity. • Friction from water drops moving in cloud builds up charges • Bottom of cloud becomes negative (induced pos. charge on Earth’s surface)

20. Lightning cont. • Electrons are attracted to the pos. charge and are transferred when lightning bolt occurs. • Will occur cloud to cloud and cloud to ground.

21. Materials that will pick up electrons (become neg.) • Plastic wrap (most negative charge) • Hard rubber • Celluloid • Sulfur • Rubber balloon • Polyethylene • Polystyrene • Amber • Sealing wax • Lucite (least negative charge)

22. Materials that tend to lose electrons (become pos.) • Rabbit fur (most positive charge) • Glass • Mica • Nylon • Wool • Cat fur • Silk • Paper • Cotton (least positive charge)

23. 21-3 Electric current • pp. 600-606

24. Potential difference • Potential difference is the difference in potential between two places • Aka: voltage • Flow from areas of high potential energy (PE) to areas of lower potential energy (PE) • Unit of measurement is volts (v) • Volts are measured with a voltmeter.

25. Circuits • A closed path through which electrons flow.

26. Current • The flow of electrons through a conductor. • The strength of the current is dependent on the number of electrons passing a point at a given time. • Unit of measurement is ampere (A) • Current is measured with an ammeter. • 1 amp = 1 coulomb/second, 1 coulomb is the charge carried by 6.24 billion billion electrons.

27. Dry Cell battery • A battery that generates electric current through a chemical reaction (using a paste).

28. Wet Cell battery • Battery made of a series of two connected metal plates, made of two different metals submerged in an electrolyte fluid (sulfuric acid commonly)

29. Resistance • The tendency of a material to oppose the flow of electrons. • Aka “electrical friction” • Units of measurement are ohms (Ω) • A thick wire will have lower resistance than a thin wire. Why?

30. Ohm’s Law • States that the current (amps) is equal to the potential difference (volts) divided by the resistance (ohms). • Current = potential difference resistance I = V/R

31. V I R Ohm’s Law circle

32. 21-4 Electrical Circuits • pp. 608-611

33. Series Circuit • Current has only one path it can travel along. • Example: Christmas tree lights, one goes out they all go out.

34. Parallel Circuit • Contains separate branched for current to move through. • Current will move through the path of lowest resistance • Potential difference will be the same across each branch of the circuit.

35. Fuses vs. Circuit breakers • Fuses: when the current becomes too strong and the fuse heats up, then the fuse will not work and will need to be replaced. • Circuit breakers: when the current becomes too strong and it heats up, then a wire will bend causing the circuit to be shut off.

36. Circuit symbols • See overhead notes

37. 21-5 Electrical Power and Energy • Pp. 614-617

38. Electrical Power • It is the rate at which electrical energy is converted to another form of energy. • Units of measurement: watts (W) or kilowatts (kW) • Formula: Power = current x voltage P = I ( V )

39. Electrical Energy • How much energy in kilowatts is used during a time period. • Units of measurement: kilowatt-hours (kWh) • Kilowatt-hour is 1000 watts of power used for 1 hour time. • Formula: elec. energy = power x time

47. INSIDE THE NUCLEUS • PROTONS POSITIVELY CHARGED • NEUTRONS NO CHARGE AT ALL

48. WHAT IS A FORCE? • It is a push or pull by an object on another object. • Unbalanced forces move matter.