Electric Circuits

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

Drift Velocity

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?

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

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

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

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

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

Conditions Necessary for Current Complete Circuit A closed path which charged particles move along.

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

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

Conditions Necessary for Current 4. Resistance If resistance were not present the circuit would overheat and burn out.

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

Factors that Effect Resistance Less Resistance More Resistance Length Cross-sectional area Material Temperature

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

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

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?

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

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?

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

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.

Ohm's Law

Ohm's Law

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

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.

Ammeters & Voltmeters in a Circuit

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)

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)

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

A Simple Circuit Model A Water Analogy

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

How is a battery different from a cell? A battery is just two or more cells wired together.

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.

Battery Terminals

Two Types of Current

Two Types of Current

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

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).

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)

Steps for Drawing Schematic Diagrams When the path of the current reaches a resistor or other device, draw the appropriate symbol with values.

Steps for Drawing Schematic Diagrams 4. Follow the current path until you reach the other terminal of the battery.

Drawing Circuit Schematic Diagrams

3.0 Ω 1.5 V

Energy Transfer & Transformation

Power Power (P) – the rate of conversion of electrical energy. Units – Watts (W)

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

Cost of Electrical Energy

Energy Transmission

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

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

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

Influencing the Flow Rate (Current) on a Tollway

Resistors in Series Circuits

Resistors in Series Circuits

Resistors in Series Circuits

Resistors in Parallel Circuits

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

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

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

Circuit Segments

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

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

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