# ch. 7 - electricity sps10. students will investigate the properties of electricity and magnetism. a....

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• Ch. 7 - ElectricitySPS10.Students will investigate the properties of electricity and magnetism. a. Investigate static electricity in terms of friction, induction, conductionb. Explain the flow of electrons in terms of alternating and direct current. the relationship among voltage, resistance and current. simple series and parallel circuits.

• Ch. 7 - ElectricityI. Electric Charge Static ElectricityConductorsInsulatorsElectroscope

• A. Static ElectricityStatic Electricitythe net accumulation of electric charges on an objectElectric Fieldforce exerted by an e- on anything that has an electric chargeopposite charges attractlike charges repel

• A. Static ElectricityStatic Dischargethe movement of electrons to relieve a separation in charge

• A. Static ElectricityThree ways to achieve static electricity

Friction Rubbing together two objects

InductionInducing a positive or negative charge

ConductionTransferring a positive or negative chargeDemo on Static Electricity

• B. ConductorsConductormaterial that allows electrons to move through it easilye- are loosely held ex: metals like copper and silver

• C. InsulatorsInsulatormaterial that doesnt allow electrons to move through it easilye- are tightly heldex: plastic, wood, rubber, glass

• D. ElectroscopeElectroscopeinstrument that detects the presence of electrical chargesleaves separate when they gain either a + or - charge

• Ch. 7 - ElectricityII. Electric CurrentCircuitPotential DifferenceCurrentResistanceOhms Law

• A. CircuitCircuitclosed path through which electrons can flow

• A. Potential DifferencePotential Difference (voltage)difference in electrical potential between two placeslarge separation of charge creates high voltagethe push that causes e- to move from - to +measured in volts (V)

• B. CurrentCurrentflow of electrons through a conductordepends on # of e- passing a point in a given timemeasured in amperes (A)

• C. ResistanceResistanceopposition the flow of electronselectrical energy is converted to thermal energy & lightmeasured in ohms ()

• C. ResistanceResistance depends onthe conductorwire thicknessless resistance in thicker wireswire length less resistance in shorter wirestemp - less resistance at low temps

• E. Ohms LawOhms LawV = I RV: potential difference (V)I: current (A)R: resistance ()Voltage increases when current increases.Voltage decreases when resistance increases.

• E. Ohms LawA light bulb with a resistance of 160 is plugged into a 120-V outlet. What is the current flowing through the bulb?GIVEN:R = 160 V = 120 VI = ?WORK:V= I * RDivide both sides by RI = V RI = (120 V) (160 )I = 0.75 A

• E. Ohms LawA cell phone with a resistance of 50 is plugged into a 110-V outlet. What is the current flowing through the bulb?GIVEN:R = 50 V = 110 VI = ?WORK:V= I * RDivide both sides by RI = V RI = (110 V) (50 )I = 2.2 A

• E. Ohms LawA Television is plugged into a 120-V outlet. How much resistance does it have if the current is measured to be 4.25 A?GIVEN:R = ? V = 120 VI = 4.25WORK:V= I * RDivide both sides by RR = V IR = (120 V) (4.25 A)R = 28.2

• Ch. 7 - ElectricityIII. Electrical CircuitsCircuit componentsSeries circuitsParallel circuitsHousehold circuits

• A. Circuit ComponentsA - batteryC - light bulbB - switchD - resistor

• B. Series CircuitsSeries Circuitcurrent travels in a single pathone break stops the flow of currentcurrent is the same throughout circuit lights are equal brightnesseach device receives a fraction of the total voltage get dimmer as lights are added

• C. Parallel CircuitsParallel Circuitscurrent travels in multiple pathsone break doesnt stop flowcurrent varies in different branchestakes path of least resistancebigger light would be dimmereach device receives the total voltageno change when lights are added

• D. Household CircuitsCombination of parallel circuitstoo many devices can cause wires to overheatSafety Features:fuse - metal melts, breaking circuitcircuit breaker - bimetallic strip bends when hot, breaking circuit

• Ch. 7 - ElectricityIV. Measuring Electricity

Electrical PowerElectrical Energy

• A. Electrical PowerElectrical Powerrate at which electrical energy is converted to another form of energyP = I VP: power (W)I: current (A)V: potential difference (V)

• A. Electrical PowerA calculator has a 0.01-A current flowing through it. It operates with a potential difference of 9 V. How much power does it use?GIVEN:I = 0.01 AV = 9 VP = ?WORK:P = I VP = (0.01 A) (9 V)P = 0.09 W

• A. Electrical PowerA flashlight has a 0.05-A current flowing through it. It operates with a potential difference of 8 V. How much power does it use?GIVEN:I = 0.05 AV = 8 VP = ?WORK:P = I VP = (0.05 A) (8 V)P = 0.4 W

• B. Electrical EnergyElectrical Energyenergy use of an appliance depends on power required and time usedE = P tE: energy (kWh)P: power (kW)t: time (h)

• B. Electrical EnergyA refrigerator is a major user of electrical power. If it uses 700 W and runs 10 hours each day, how much energy (in kWh) is used in one day?GIVEN:P = 700 W = 0.7 kWt = 10 hE = ?WORK:E = P tE = (0.7 kW) (10 h)E = 7 kWh

• B. Electrical EnergyA refrigerator is a major user of electrical power. If it uses 700 W and runs 10 hours each day, how much energy (in kWh) is used in one day?GIVEN:P = 900 W = 0.9 kWt = 14 hE = ?WORK:E = P tE = (0.9 kW) (14 h)E = 12.6 kWh

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