Presentation on theme: "0016: Electricity and Magnetism 1"— Presentation transcript:
10016: Electricity and Magnetism 1 0016: Electricity and Magnetism 1. recognize the characteristics of static electricity
2Electricity describes charged particles Rub a balloon with wool, picks up electronsRub glass with silk, loses electronsObjects attract or repel when “electrically charged”“static electricity”
3Figure 5-1The two kinds of electrical charges. Opposite charges attract, while like charges repel.
4Electricity describes charged particles These charged particles can be at rest (“static electricity”)or they may be moving(“current electricity”)
5Coulomb’s LawThe electric force between two charged particles varies directly as the product of their charges and inversely as the square of the separation distances.force (newtons) = k x 1st charge x 2nd charge / distance2
6Electrical FieldA kind of “aura” or “force field” around every electric chargeExtends radially awayfrom the proton andin opposite directionabout the electron.
7…distinguish between conductors and insulators Material that electrons are able to pass throughMetals, ionic solutionsInsulatorsMaterial that electrons do not through easilyGlass, wood, rubber, plastics
80016: Electricity and Magnetism 2 0016: Electricity and Magnetism 2. demonstrate knowledge of the components of an electric circuit and their functions.
9Electrical potential and electric current Movement of electric charge creates electric currentCharges move as current only when energy is supplied to themCircuitSwitchVoltageCurrent
10If we use the water analogy… Voltage = the pressureCurrent = the rate of flow
11Voltage The push that makes electrons move. 1.5 V “D” cell or 6 V lantern batteryHigher voltage = greater push on electronsWater analogyVoltage causes current.
12Electric Current Voltage creates current Current is the amount of charge passing a point in a circuit in a secondMetric unit = Ampere (A)Measures by an ammeterDifferent devices often carry different amounts of current
13…distinguish between DC and AC Direct currentCurrent moves in one directionFrom dry cells or batteriesAlternating currentPumped to us by Cobb EMCOscillates back and forth at 60 Hzwall sockets
14Ohm’s Law How is current related to voltage? Direct relation between the two led to discovery of “resistance”Voltage / Current = Resistance (V / I = R)
15Resistancemeasures how hard it is for current to move through a conductor (unit = Ohm).Easier for electrons to move through thick wires than thin wiresLight bulb filament, thin, high resistance, heats up and glows
160016: Electricity and Magnetism 3. compare series and parallel circuits.
18…distinguish between Series Circuits & Parallel Circuits Only one path for current flowSame amount of current thru entire circuitCheap string of decorative lightsAlternate paths for current flowCurrent divides up among the pathsWiring system for lights and elec outlets in homes & buildings
21Electric Power Power = energy used / time Also calculated as product of current and voltageWatts = amp’s x voltsEx: 60W bulb draws .5 A on a 120V line120W lamp draws 1A on a 120V lineIf a 120V line to a socket is limited (by a fuse) to 15A, will it operate a 1200W dryer?
220016: Electricity and Magnetism 4 0016: Electricity and Magnetism 4. identify properties of magnets and characteristics of magnetic fields.
23Magnetism Children are fascinated by magnets! “floating” paper clip “jumping” nails“iron filing” cartoon hair
24The little fridge magnet reminds us that the magnetic force on Earth is stronger than gravity.
25magnetism Magnesia, province of Greece Unusual property of lodestone noted over 2000 years ago
2612th C, Magnets first used in navigational compass, Chinese
2716th C, William Gilbert“Every magnet has two poles, a north and a south.”“Like magnetic poles repel, unlike poles attract.”
28Figure 5-3A compass needle and the Earth. Any magnet will twist because of the forces between its poles and and those of the Earth. Every magnet has at least two poles.
29Courtesy Andy WashnikFigure 5-5(b)Iron filings placed near a bar magnet align themselves along the field.
30Figure 5-4A magnetic field. Small magnets placed near a large one orient themselves along the lines of the magnetic field, as shown.
31Figure 5-5(a)A bar magnet and its magnetic dipole field.
32“Opposites attract. Likes repel.” The above describes both magnetic and electric force, butelectric charges can be isolated,magnetic poles cannot.
33Figure 5-6Cut magnets. If you break a dipole magnet in two, you get two smaller dipole magnets, not an isolated north or south pole.
340016: Electricity and Magnetism 5 0016: Electricity and Magnetism 5. demonstrate knowledge of the relationship between moving electric charges and magnetic fields and applications of electromagnets in everyday life (e.g., motors, generators)
351820, Hans Oersted…connected a battery to let electric current flow, and noticed a compass needle twitch and move.
36Electricity & Magnetism: “ two sides of the same coin “ Every time an electric charge moves, a magnetic field is created.(electromagnet)Every time a magnetic field varies, an electric field is created.(hydroelectic dams)
37Electric motors convert electricity into magnetic fields, for useful rotary motion
38Figure 5-8An electric motor. The simplest motors work by placing an electromagnet that can rotate between two permanent magnets.(a) When the current is turned on, the north and south poles of the electromagnet are attracted to the south and north poles of the permanent magnets. (b)–(d) As the electromagnet rotates, the current direction is switched, causing the electromagnet to continue rotating.
39Electric motors convert electricity into magnetic fields, for useful rotary motion
40Electrical Generators …are the exact opposite of electric motors: they convert rotary motion into electrical energy.link
41Energy Transformation - kinetic energy of moving water can be used to turn a wheel that runs the mill to grind grain.
42Energy Transformation Wind can be used to vary a magnetic field about wires, to generate alternating current.
43We can burn coal to heat water to produce steam to turn a turbine to vary a magnetic field about wires, to generate alternating current. (coal-fired power plant)
44We can dam rivers, then release energy from the lake side, to turn a turbine, to vary a magnetic field about wires, to generate alternating current. (hydroelectric energy)
45We control nuclear fission reactions to heat water to produce steam to turn a turbine to vary a magnetic field about wires, to generate alternating current. (nuclear energy)
46In some parts of the world, we can use heat from the Earth to produce steam to turn a turbine to vary a magnetic field about wires, to generate alternating current. (geothermal energy)
47Anything that can turn an axle can power a generator. Flowing water, pressurized steam, wind, or a gasoline engine can drive a rotating turbine that houses coils of copper wire.