Physical Science Goal 4 Notes

1. Physical ScienceGoal 4 Notes

2. Brain Pop: Electricity • http://glencoe.mcgraw-hill.com/sites/0078802482/student_view0/brainpop_movies.html

3. Electricity • Static electricity is the build up of an electrical charge. • For electrically charged materials, opposites charges attract, while like charges repel.

4. http://glencoe.mcgraw-hill.com/sites/0078807220/student_view0/chapter20/concepts_in_motion.htmlhttp://glencoe.mcgraw-hill.com/sites/0078807220/student_view0/chapter20/concepts_in_motion.html

5. Electricity • Electricity is moving electrons.

6. Conductors allow electrons to move freely through them. • Objects are grounded when they are connected to the earth or ground by a good conductor. • Insulators are materials that do not allow electrons to move freely through them.

7. Voltage – Potential Difference • The electrical potential is the potential energy difference per unit charge. • The potential difference is the difference in potential between two places. • Units for potential difference are volts (V).

8. Electrical Potential Difference • http://glencoe.mcgraw-hill.com/sites/0078807220/student_view0/chapter21/concepts_in_motion.html

9. Potential difference can be referred to as voltage and is measured with a voltmeter. • Voltage is a comparison of the energy carried by electrons at different points.

10. Circuit • Circuit is a closed path through which electrons flow. • Current is the flow of electrons through a wire or conductor. • Units for current are amperes (A) as is a measure of the number of electrons passing a point in a given time.

11. Batteries • Dry cell - Electron pump with a potential difference between the positive and negative terminals. • Zinc container with a moist chemical paste with a solid carbon rod in the center. The paste contains MnO2 (manganese dioxide), NH4Cl (ammonium chloride) and C (carbon) which reacts with the zinc.

12. B. Wet cell - Contain metal plates placed in a chemical solution (electrolyte). Ex.: Car battery – lead storage battery. Plates of lead (Pb) and lead dioxide (PbO2) in sulfuric acid (H2SO4) solution. The car battery has 6 cells with a potential of 2 V each for a total of 12 V.

13. Copper - low resistance Tungsten - high resistance Resistance • Resistance is a materials ability to oppose the flow of electrons causing it to change electrical energy into thermal energy and in some cases light. • Resistance is measured in ohms (Ω).

14. All conductors, except superconductors at very low temperatures, have some resistance. • For a given material, resistance is increased as length increases; decreases as thickness increases; and, usually increases as temperature increases.

15. Ohm’s Law Potential difference = current X resistance V = I R Units V = potential difference volts (V) I = current amperes (A) R = resistance ohms (Ω)

16. Resistance and Ohm’s Law • http://glencoe.mcgraw-hill.com/sites/0078807220/student_view0/chapter22/concepts_in_motion.html

17. Voltage increases when current increases. • Voltage decreases when resistance increases

18. Flash Card

19. Circuits • http://glencoe.mcgraw-hill.com/sites/0078807220/student_view0/chapter22/concepts_in_motion.html

20. Circuits • Series circuit – only one path for the electricity 2. Parallel circuit – More than one path for the electricity with each branch having the same potential difference. 3. Complex circuit – contains both series circuits and parallel circuits

21. Series Circuits • Parallel Circuits

22. 3. Open circuit – when a switch is opened (turned off) or a bulb burns out the current no longer flows through that path, therefore the circuit is open. 4. Closed circuit – when a switch is closed (turned on) and bulbs burn the current flows through the path (s), therefore the circuit is closed.

23. Safety Devices • Fuses and circuit breakers are safety devices to prevent a circuit from overheating and causing a fire. • Fuses have a metal strip that melts when the circuit gets too hot, causing the circuit to open. • Fuses can only be used once and must be replaced with the same size and type of fuse. • Fuses can explode if they get too hot and cause fires.

24. Fuses

25. Breakers • Circuit breakers contain a metal strip that bends as it heats up and trips the breaker switch to open the circuit. • Breakers can be reset several times before they have to be replaced. • Like fuses breakers come in different sizes. • Main breakers control the flow of electricity into the house. • When they are thrown (or tripped) there will be no electricity in the house or building.

26. Breakers

27. Electrical Power Electrical power is the rate at which electric energy is converted into another form of energy. Electric Power = current X voltage PE = I V Units PE = electric power watts (W) or kW I = current amperes (A) V = voltage volts (V) One watt of electric power is produced when one ampere of current flows through a circuit with a potential difference of one volt.

28. Flash Card

29. Electrical Energy Electrical Energy is calculated by multiplying the electrical power by the amount of time the power was used. Energy = power X time E = P t Units E = electrical energy kilowatt-hours (kWh) P = electrical power kilowatt (kW) t = time hours (h) One kilowatt-hour (kWh) is 1000 watts of power used in one hour.

30. Flash Card

31. Electricity • http://www.teachertube.com/view_video.php?viewkey=30f4d56a2f1e1e760e53

32. Brain Pop: Magnetism • http://glencoe.mcgraw-hill.com/sites/0078802482/student_view0/brainpop_movies.html

33. Magnets • Magnets point north – south when suspended from a string and align with the Earth’s magnetic north and south poles. • Magnetism is a force of attraction and repulsion between like and unlike poles. • Magnetic poles are at the ends and are the area of strongest attraction.

34. Permanent magnets retain their properties for a long time and are made of iron (Fe), nickel (Ni) or cobalt (Co). • Magnetite is a mineral with natural magnetic properties. • Lodestone is a natural magnet. • Magnetism can be conducted through paper clips and nails to make temporary magnets. • Temporary magnets lose the magnetic properties after being removed from the magnet.

35. Magnetic Fields Magnetic field is the area around a magnet where the magnetic forces act. • They are strongest near the poles. • The Earth’s magnetic north pole is near the south pole and the Earth’s magnetic south pole is near the north pole.

36. Magnetic Domains • In order to form a magnet, the magnetic poles of the atoms must align. • Magnetic domains are groups of atoms with aligned magnetic poles. • Permanent magnets can lose their domains if heated or dropped. • When a permanent magnet is cut into smaller pieces, each piece will have its own poles.

37. Compass is an instrument for determining direction that contains a magnetized needle to point to the Earth’s magnetic poles.

38. 1820, Hans Christian Oersted, Danish physics teacher, observed that current passing through a wire produced a magnetic field that could be detected by a compass, and that the direction of the magnetic field reversed when the direction of the electric current reversed.

39. Electromagnets Electromagnets are strong temporary magnets produced by inserting an iron core into a coil of wire and passing an electric current through the wire. • Strength of electromagnets can be changed by changing the number of coils in the wire or the amount of current going through the wire. • Uses for electromagnets: loudspeaker, doorbells, lifting metal objects, meters, toys, and motors.

40. Galvanometers • Galvanometer is an instrument used to detect electrical current. • Ammeter is a galvanometer that measures current and is connected in series in the circuit. • Voltmeter is a galvanometer that measures potential difference and is connected in parallel in the circuit.

41. Electromagnetic induction • 1831, Michael Faraday, British scientist, and Joseph Henry, American scientist, working independently found that by moving a wire in and out of a magnetic field that they could produce an electric current. • Electromagnetic induction is the production of an electrical current by moving a wire through a magnetic field.

42. Generators Generators produce electricity by rotating a loop of wire in a magnetic field. • The wire loop is rotated by a mechanical energy source. • This produces alternating current because the current changes direction each time the wire passes a different pole.

43. Turbines are large wheels that rotate when pushed by water, wind, or steam. • The steam can be produced by burning of fossil fuels or nuclear reactions.

44. Types of Current • DC – direct current flows in one direction • AC – alternating current reverses the direction of flow in a regular pattern • In the US, our current has a frequency of 60 Hz and changes direction 120 times/sec.

45. Transformers Transformers reduce or increase voltage of alternating current. Transformers contain 2 coils of wire (primary coil – incoming current and secondary coil – outgoing current) wrapped around an iron core.

46. 2 Types of Transformers • Step-up transformers have more coils of wire on the secondary coil and increase the voltage. • Step-down transformers have more coils of wire on the primary coil and decrease the voltage.

47. Superconductors • 1911, Heike Kamerlingh Onnes, a Danish physicist, discovered that at low temperatures some materials lose their electrical resistance. • Since the material loses its electrical resistance at low temperatures it is called a superconductor.

48. The temperature at which the superconductor loses its electrical resistance is its critical temperature. • Most of these temperatures are near absolute zero -273 °C. • Liquid helium (4.2 K or -268.2 °C) was used to cool the first superconductors.

49. 1987, J.G.Bednorz and K.A.Müller produced a superconductor from a ceramic material with a critical temperature of 30 K (-243 °C). • We now have superconductors with critical temperatures at 130 K (-143 °C) and use liquid nitrogen (-196 °C) to cool the material because it is cheaper.

50. Superconductors are more efficient because they do not lose energy due to resistance. • Research continues to build superconductor that is less brittle and more flexible and thinner.