Current ( I ) – the rate at which charge passes through a wire.

Units – C/s = Amperes (A)

ΔqI=

t

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. 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?

1.5 s

DC – charges move only in one direction.

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

1. Complete Circuit• A closed path which charged particles

move along.

2. Potential difference between two points in the circuit.

• May be supplied by a battery (has + and – terminals)

3. Conductive material through which charge can move.

• Metals are good conductors because their electrons move easily.

4. Resistance• If resistance were not present the

circuit would overheat and burn out.

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

Unit – Ohm (Ω)

FactorLess

ResistanceMore

Resistance

Length

Cross-sectional area

Material

Temperature

Resistivity ( ρ ) – a measurement of how conductive a material is. (High resistivity means not as conductive)

Unit - Ω•m

ρLR=

A

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. What is the resistance in the wire?

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 8.23x10-6m2 and a resistance of 0.125Ω. What is the wire made out of?

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

Nichrome

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

VR=

I

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

Picture Symbol

Voltmeter – a device used to measure potential difference across a circuit.

Connect outside the direct path of the current (parallel connection)

Ammeter – a device used to measure the current through a circuit.

Connect in the direct path of the current (series connection)

A Water Analogy

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

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

2. Draw a wire coming out of the power source.

Draw wires as straight lines (use a ruler if needed)

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

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

1.5 V

3.0 Ω

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

Units – Watts (W)

22 V

P=IV=I R = R

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

Units – Joules (J)

22 V t

W = Pt=VIt=I Rt=R

QuantityQuantity SymbolSymbol UnitUnit FormulaFormula

Resistance

Voltage(Potential Difference)

Charge

Current

Power

Energy

Characteristics Series Circuit

Number of Paths

Current

Potential Difference (Voltage)

  

Total Resistance 

Power

Disconnecting one bulb

 

Characteristics Parallel Circuit

Number of Paths

Current 

Potential Difference (Voltage)

  

Total Resistance 

Power

Disconnecting one bulb

 

 

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.

Segment – part of a circuit with two or more resistors

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

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

Junction A Junction B Junction C

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