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Electric Circuits

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Electric Current Current ( I ) – the rate at which charge passes through a wire. Units – C/s = Amperes (A)

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Drift Velocity

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**There is 3A of current moving through a point on a wire**

There is 3A of current moving through a point on a wire. How much charge passes that point in 30 seconds?

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**There is 3A of current moving through a point on a wire**

There is 3A of current moving through a point on a wire. How much charge passes that point in 30 seconds? 90C

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**How long does it take a wire carrying a current of 10A to move 15C of charge?**

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**How long does it take a wire carrying a current of 10A to move 15C of charge?**

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Types of Current DC – charges move only in one direction.

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Types of Current AC – the motion of charges continuously changes in the forward and reverse directions.

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**Conditions Necessary for Current**

Complete Circuit A closed path which charged particles move along.

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**Conditions Necessary for Current**

2. Potential difference between two points in the circuit. May be supplied by a battery (has + and – terminals)

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**Conditions Necessary for Current**

3. Conductive material through which charge can move. Metals are good conductors because their electrons move easily.

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**Conditions Necessary for Current**

4. Resistance If resistance were not present the circuit would overheat and burn out.

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Resistance Resistance ( R ) – the opposition that a device or conductor presents to the flow of electric current. Unit – Ohm (Ω)

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**Factors that Effect Resistance**

Less Resistance More Resistance Length Cross-sectional area Material Temperature

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Resistivity Resistivity ( ρ ) – a measurement of how conductive a material is. (High resistivity means not as conductive) Unit - Ω•m

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**R- Resistance (Ω) ρ- Resistivity (Ω·m) L- Length of wire (m) A- Cross-sectional Area (m2) **

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**A 6. 5m long copper wire has a cross-sectional area of 3x10-3m2**

A 6.5m long copper wire has a cross-sectional area of 3x10-3m2. What is the resistance in the wire?

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**A 6. 5m long copper wire has a cross-sectional area of 3x10-3m2**

A 6.5m long copper wire has a cross-sectional area of 3x10-3m2. What is the resistance in the wire? R = 3.7x10-5Ω

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**A 0. 686m long wire has a cross sectional area of 8**

A 0.686m long wire has a cross sectional area of 8.23x10-6m2 and a resistance of 0.125Ω. What is the wire made out of?

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**A 0. 686m long wire has a cross sectional area of 8**

A 0.686m long wire has a cross sectional area of 8.23x10-6m2 and a resistance of 0.125Ω. What is the wire made out of? Nichrome

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Ohm's Law Ohms’s Law – the ratio of the potential difference to the current is always a constant for a given conductor and is called resistance.

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Ohm's Law

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Ohm's Law

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Resistors Resistor – a device used in a circuit to limit current flow or provide a potential drop. Picture Symbol

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Variable Resistor – a coil of resistance wire whose effective resistance can be varied by sliding a contact point. As more of the coil is used in the circuit, the resistance of the circuit increases, the current decreases.

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**Ammeters & Voltmeters in a Circuit**

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**Ammeters & Voltmeters in a Circuit**

Voltmeter – a device used to measure potential difference across a circuit. Connect outside the direct path of the current (parallel connection)

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**Ammeters & Voltmeters in a Circuit**

Ammeter – a device used to measure the current through a circuit. Connect in the direct path of the current (series connection)

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Overload If a 1 appears by itself on the far left the multimeter has overloaded. Try going to a higher setting If at highest setting, record Overload or OL on lab

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A Simple Circuit Model A Water Analogy

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What is a cell? A cell (wet or dry), a contained area that releases energy due to a chemical reaction. A cell stores charges.

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**How is a battery different from a cell?**

A battery is just two or more cells wired together.

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**What is the difference between a D and AA cell?**

Both cells do 1.5 J of work for each Coulomb of charge moved from one side to the other However, a D cell stores more coulombs of charge, so it will last longer and do more work overall.

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Battery Terminals

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Two Types of Current

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Two Types of Current

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**Drawing Circuit Schematic Diagrams**

Circuit Schematic – a diagram of an electric circuit using standard symbols for the circuit elements.

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**Steps for Drawing Schematic Diagrams**

Begin by drawing the symbol for the battery or other source of electric energy (such as a cell or generator).

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**Steps for Drawing Schematic Diagrams**

2. Draw a wire coming out of the power source. Draw wires as straight lines (use a ruler if needed)

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**Steps for Drawing Schematic Diagrams**

When the path of the current reaches a resistor or other device, draw the appropriate symbol with values.

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**Steps for Drawing Schematic Diagrams**

4. Follow the current path until you reach the other terminal of the battery.

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**Drawing Circuit Schematic Diagrams**

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3.0 Ω 1.5 V

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**Energy Transfer & Transformation**

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**Power Power (P) – the rate of conversion of electrical energy.**

Units – Watts (W)

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Electrical Energy Electrical Energy (W) – the energy made available by the flow of electrical charges through a conductor Units – Joules (J)

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**Cost of Electrical Energy**

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Energy Transmission

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**(Potential Difference)**

Quantity Symbol Unit Formula Resistance Voltage (Potential Difference) Charge Current Power Energy

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**Resistors in Series Circuits**

Characteristics Series Circuit Number of Paths Current Potential Difference (Voltage) Total Resistance Power Disconnecting one bulb

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**Resistors in Parallel Circuits**

Characteristics Parallel Circuit Number of Paths Current Potential Difference (Voltage) Total Resistance Power Disconnecting one bulb

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**Influencing the Flow Rate (Current) on a Tollway**

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**Resistors in Series Circuits**

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**Resistors in Series Circuits**

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**Resistors in Series Circuits**

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**Resistors in Parallel Circuits**

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**c. Fill in the current in the eight blank spaces in the view of the same circuit shown above.**

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**3. Cross out the circuit below that is not equivalent to the circuit above.**

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Circuit Segments Segment – part of a circuit with two or more resistors

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Circuit Segments

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Circuit Switches In which, if any, of the circuits below will the lamp light when switch S is closed?

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**Junctions Junction – a point where two or more current paths join.**

Junction B Junction C

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Junctions Kirchoff’s Junction Rule - The total current directed into a junction must equal the total current directed out of the junction. Junction D Junction E Junction F

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