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Electricity – Potential, Power, and Resistance

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Drill #25 Quote: A goal is a dream with a deadline. ~Napoleon Hill Objective:TAKS Warm-up Potential, Power, Resistance Fun w/ Electricity TAKS question: In animal cells like the one shown above, which organelle is used for storing water? F Nucleus G Mitochondrion H Ribosome J Vacuole

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What is an electric field??? It is an area of influence around a charged object.It is an area of influence around a charged object. Positively charged objects within that field will experience an electrical force. Positively charged objects within that field will experience an electrical force. + + + + + + + + + ++ + Electric Field Test Charge Electric Field - - - - - - - -- - - - - - - FF

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Electric Potential Energy Review –Potential energy = mgh Based on height –Charges naturally move from higher to lower To move a charge against natural direction in relation to electric field = WORK! Same applies to electricity! (related to placement of charge in electric field)

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Electric Potential Dependent solely on location of charge… –E potential = PE Q (charge) + positive- negative

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To light a bulb, two different circuits are at work! –External (wiring) –Internal (battery) Movement of charge from PE to PE The Electric Potential Difference = Voltage = Volts = 1 Joule energy / Coulomb of charge Circuitry V final – V initialWork charge ∆PE charge ==

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Electric Current The rate at which electrical charges flow through a wire or conductor is called electric current.The rate at which electrical charges flow through a wire or conductor is called electric current. Electrical current = charge passing through a given area / time I = Δ q/ Δt SI Unit = C/s = Amperes (A)

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Practice 1. A current is said to exist whenever _____. a. a wire is charged b. a battery is present c. electric charges are unbalanced d. electric charges move in a loop 2.The diagram at the right depicts a conducting wire. Two cross-sectional areas are located 50 cm apart. Every 2.0 seconds, 10 C of charge flow through each of these areas. The current in this wire is ____ A. D. Current is the ratio of charge to time. The quantity of charge passing through a cross section in 2 seconds is 10 C. The ratio of charge to time is I = Q / t = ( 10 C) / ( 2 s) = 5 C/s = 5 Ampere

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Current Positive charges = carriers of charge –In most cases! Current = direction that positive charges move in… –Electrons move in opposite direction

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Electrical Power Rate at which energy is added/removed from a circuit Measured in wattage (W) –Do not confuse with W for work! Wattage = 1 Joule sec Power = Work = energy consumed Time Time

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Electrical Power Power = rate at which energy is added/removed from a circuit by a battery or a load. Current = rate at which charge moves within a circuit. Electric potential difference = potential energy difference per charge between two points. Then…….

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Practice Determine the... a.... current in a 60-watt bulb plugged into a 120-volt outlet. b.... current in a 120-watt bulb plugged into a 120- volt outlet. c.... power of a saw that draws 12 amps of current when plugged into a 120-volt outlet. d.... power of a toaster that draws 6 amps of current when plugged into a 120-volt outlet. e.... current in a 1000-watt microwave when plugged into a 120-volt outlet.

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Practice a. The current in a 60-Watt bulb plugged into a 120-Volt outlet is 0.5 A. I = P / V = (60 W) / (120 V) = 0.5 A b. The current in a 120-Watt bulb plugged into a 120- Volt outlet is 1.0 A. I = P / V = (120 W) / (120 V) = 1.0 A c. The power of a saw that draws 12 amps of current when plugged into a 120-Volt outlet is 1440 W. P = V I = (120 V) (12 A) = 1440 W d. The power of a toaster that draws 6 amps of current when plugged into a 120-Volt outlet is 720 W. P = V I = (120 V) (6 A) = 720 W e. The current in a 1000-Watt microwave when plugged into a 120-Volt outlet is 8.3 A.

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Resistance - the tendency for a material to oppose the flow of electronsResistance - the tendency for a material to oppose the flow of electrons - All materials have some electrical resistance. - Resistance depends on length, cross- sectional area, material, and temperature Ex. Making wires thinner, longer, or hotter increases the resistance. Resistance

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Resistors provide a specified amount or resistance to a conductor. Used to regulate the amount of current in a conductor. Resistors

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Ohm’s law - the current in a circuit (I) equals the voltage difference (V) divided by the resistance (R). R = V/I Resistance is measured in ohms . Ohm’s Law

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Sample Problem The resistance of a steam iron is 19.0 Ω. What is the current in the iron when it is connected across a potential difference of 120 V? R = V/I V= 120 V R= 19 Ω I = V/R = 120 V / 19 Ω = 6.32 A

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Electrical Power revisited…. Electrical Power is the rate at which electric charge converts electrical potential energy to non-electrical forms of energy. P = IΔV = I²R = ΔV²/R SI Unit = watt (W)

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Sample Problem An electric space heater is connected across a 120 V outlet. The heater dissipates 1320 W of power in the form of electromagnetic radiation and heat. Calculate the resistance of the heater. V= 120 VP = 1320 W P = ΔV²/R R = ΔV²/P = (120 V)²/ 1320 W = 10.9 Ω

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Electric Power Electric companies measure energy consumed in kilowatt-hours (kW h)

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Electric Power How much does it cost to operate a 100.0 W light bulb for 24 h if electrical energy costs $0.080 per kWh? Total Energy Used = (0.100 kW)( 24 h) = 2.4 kWh Cost = (2.4 kWh)($ 0.080/ kWh) = $0.19

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