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Electric Circuits Mrs. Cockrell PAP Physics

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Electric Current Flow of electrical charge Flow of electrical charge The rate at which electric charges move through a given area. The rate at which electric charges move through a given area. Formula Formula I = q/t I = q/t I = current (A) I = current (A) q = charge (C) q = charge (C) t = time (s) t = time (s)

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DC vs AC Direct Current (DC) Direct Current (DC) All charges move in one direction from an area of high potential to an area of low potential All charges move in one direction from an area of high potential to an area of low potential Alternating Current (AC) Alternating Current (AC) Charges move back and forth generating a flow of charge Charges move back and forth generating a flow of charge

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Conventional Current vs Flow of Electrons Conventional Current – Flow of positive charges Conventional Current – Flow of positive charges Flow of electrons – Movement of electrons Flow of electrons – Movement of electrons They are opposite directions of each other They are opposite directions of each other

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Sources of Current Battery – Uses chemical energy to generate DC current Battery – Uses chemical energy to generate DC current Photovoltaic Cell (Solar Cell) – Converts sunlight into DC current Photovoltaic Cell (Solar Cell) – Converts sunlight into DC current An inverter changes it to AC An inverter changes it to AC Generators – Converts kinetic energy into AC. Generators – Converts kinetic energy into AC.

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Potential Difference Caused by a separation of opposite charges Caused by a separation of opposite charges Often times called Voltage or electric potential Often times called Voltage or electric potential

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Resistance The opposition to electron flow through a conductor The opposition to electron flow through a conductor Resistance is affected by length, area, type of material, and temperature Resistance is affected by length, area, type of material, and temperature

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Ohms Law Formula Formula V = IR V = IR V = Potential Difference (V) V = Potential Difference (V) I = Current (Amperes or Amps) I = Current (Amperes or Amps) R = Resistance (Ohms or Ω) R = Resistance (Ohms or Ω) Example Example A 1.5 V battery is connected to a small light bulb with a resistance of 3.5Ω. What is the current in the bulb? A 1.5 V battery is connected to a small light bulb with a resistance of 3.5Ω. What is the current in the bulb?

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Kilowatt-Hour How electric companies charge for service. How electric companies charge for service. You pay for energy used, not power. You pay for energy used, not power. 1KW-Hr = 3.6 x 10 6 J 1KW-Hr = 3.6 x 10 6 J Example: Example: A television set draws 2.0 A when operated on 120 V. (A) How much power does the set use? (B) If the set is operated for an average of 7.0 h/day, what energy in kWh does it consume per month? (30 days) (C) At 11 cents per kWh, what is the cost to operate the set per month? A television set draws 2.0 A when operated on 120 V. (A) How much power does the set use? (B) If the set is operated for an average of 7.0 h/day, what energy in kWh does it consume per month? (30 days) (C) At 11 cents per kWh, what is the cost to operate the set per month?

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Electric Circuits Set of electrical components connected so that they provide one or more complete paths for the movement of charges Set of electrical components connected so that they provide one or more complete paths for the movement of charges Closed circuit – complete path, one in which electrons are free to move Closed circuit – complete path, one in which electrons are free to move Open circuit – not a complete path Open circuit – not a complete path Light Bulbs contain a complete conducting path Light Bulbs contain a complete conducting path

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Diagramming a circuit Schematic Diagram Schematic Diagram Graphical representation of an electrical circuit Graphical representation of an electrical circuit Wire or Conductor Resistor Bulb or Lamp Plug Battery Switch Capacitor

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Examples Draw a schematic diagram of two resistors connect in a line with a battery. Draw a schematic diagram of two resistors connect in a line with a battery.

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Series Circuit A circuit or portion of a circuit that provides a single conducting path without junctions A circuit or portion of a circuit that provides a single conducting path without junctions Current through each resistor is the same but varying potential difference Current through each resistor is the same but varying potential difference Total Resistance (Equivalent Resistance) – sum of all resistances Total Resistance (Equivalent Resistance) – sum of all resistances Sum of the voltages = total voltage Sum of the voltages = total voltage All elements must be present to get electron flow All elements must be present to get electron flow

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Example A 9.0V battery is connected to four light bulbs in series of resistances 2Ω, 4Ω, 5 Ω, and 7 Ω. Draw the schematic diagram and calculate the equivalent resistance and current in the circuit. A 9.0V battery is connected to four light bulbs in series of resistances 2Ω, 4Ω, 5 Ω, and 7 Ω. Draw the schematic diagram and calculate the equivalent resistance and current in the circuit.

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Parallel Circuits Two or more components in a circuit that are connected across common points or junctions, providing separate paths for the current. Two or more components in a circuit that are connected across common points or junctions, providing separate paths for the current. Resistors have the same potential difference but varying currents Resistors have the same potential difference but varying currents Sum of the currents = total current Sum of the currents = total current Equivalent Resistance is calculated by using the reciprocal relationship Equivalent Resistance is calculated by using the reciprocal relationship Not all elements must be present in order to operate Not all elements must be present in order to operate

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Example A 9V battery is connected to four resistors in parallel with the following resistances. 7 Ω, 5 Ω, 4 Ω, and 2 Ω. Draw the schematic diagram and find the equivalent resistance for the circuit and the total current in the circuit. A 9V battery is connected to four resistors in parallel with the following resistances. 7 Ω, 5 Ω, 4 Ω, and 2 Ω. Draw the schematic diagram and find the equivalent resistance for the circuit and the total current in the circuit.

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Complex Circuits When wiring a home or building complex circuits are used. When wiring a home or building complex circuits are used. Circuit breakers and fuses are placed in the circuits that open when the current becomes too high. Circuit breakers and fuses are placed in the circuits that open when the current becomes too high. To calculate equivalent resistance, simplify the circuit into groups of series and complex circuits To calculate equivalent resistance, simplify the circuit into groups of series and complex circuits Then find equivalent resistances of each group Then find equivalent resistances of each group Then work backwards to determine potential difference and current Then work backwards to determine potential difference and current Mrs. Cockrell sample problem Mrs. Cockrell sample problem

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Example A circuit is assembled such that a 6 ohm and 2 ohm in series with each other is in parallel with a 4 ohm resistor. This entire group is in series with a 3 ohm resistor and a 6 ohm resistor. Following the series/parallel group is a 1 ohm resistor. All attached to a 9V battery. Determine the current in and potential difference across the 2 ohm resistor. A circuit is assembled such that a 6 ohm and 2 ohm in series with each other is in parallel with a 4 ohm resistor. This entire group is in series with a 3 ohm resistor and a 6 ohm resistor. Following the series/parallel group is a 1 ohm resistor. All attached to a 9V battery. Determine the current in and potential difference across the 2 ohm resistor.

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Power The rate at which energy is transferred. The rate at which energy is transferred. P=IV P=IV P = Power (W) P = Power (W) I = Current (A) I = Current (A) V = Electric Potential (V) V = Electric Potential (V) Example: Example: A 6.0V battery delivers a 0.50 A current to an electric motor that is connected across its terminals. (A) what is the power of the motor? (B) If the motor runs for 5.0 minutes, how much energy is delivered? A 6.0V battery delivers a 0.50 A current to an electric motor that is connected across its terminals. (A) what is the power of the motor? (B) If the motor runs for 5.0 minutes, how much energy is delivered?

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