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What work is required to move 7 coulombs of charge through a potential difference of 3 volts?

Electric Current and Circuits!

Electric Current

• Electric current: flow of charge

• Not referring to the speed of the charged particles, but to the quantity of charge that passes a single point in time.

Electric Current

Coulomb

Second

Ampere (A)

Example

• What is the electric current in a conductor if 240 coulombs of charge pass through in 1.0 minute?

How do we get a current in a conductor?

A potential difference is necessary!

• Voltage: the electric potential in a circuit that provides electric pressure to push electrons through the circuit.

• A voltage source, like a battery or cell, creates a potential difference that moves these electrons.

• Voltages is measured in _______

Resistance

• Electric resistance: the resistance of an object to the flow of electric charge through it

• Like friction for particles! conversion of energy into heat

Ohm’s Law

R = VI

Volts

Ampere

Ohm (Ω)

Example

• When a conductor has a potential difference of 110 volts placed across it, the current through it is 0.50 ampere. What is the resistance of the conductor?

Resistivity (ρ)

• Property of a material that affects its resistance

• resistivity, resistance

Resistance

Resistivity

Length of the

conductor

Cross-sectional area

Example

• What is the resistance at 20°C of an aluminum wire that is 0.2 meter long and has a cross sectional area of 1.00 x 10-3 square meter? (ρ= 2.65 x10-8 Ωm)

What do we use to measure the current in a circuit?

An ammeter is placed in a circuit to measure the current. It must be in the path of the current, so that nothing flows without going through the ammeter.

What do we use to measure voltage in a circuit?

A voltmeter is placed across a circuit component to measure the voltage. Voltage does not flow; we measure the potential difference across a component to see the push each coulomb of charge feels to move through it.

The diagram below represents a simple electric circuit. How much charge passes through the resistor in 2.0 seconds?

1) 4.0 C 3) 8.0 C

2) 2.0 C 4) 6.0 C

Example

If I have a circuit hooked up to a 6-V power source, and the light bulb has a resistance of 2 Ω, find the value of the current.

1) If a 12-volt battery is hooked up to a light bulb and 2.5 amperes of current flow, calculate the resistance of the light bulb.

2) How much voltage is required for 0.02 A to flow through a resistor of 250 Ω?

3) How much current will flow through a 100-ohm resistor if it’s drawing from a source of 120 volts?

In a simple electric circuit, a 110-volt electric heater draws 2.0 amperes of current. The resistance of the heater is

1) 220 ohms 2) 28 ohms

3) 55 ohms 4) 0.018 ohms

A 9.0-volt battery is connected to a 5.0-ohm resistor as shown below. What is the current through the resistor?

1) 9.0 A 2) 5.0 A

3) 1.8 A 4) 0.55 A

Practice!

• Page 616: 2a, 3, 4• Page 627: 32, 33a, 35 • Page 628: 40-42

EXIT QUIZ

• 1. The ratio of the potential difference across a conductor to the current in the conductor is called(1) Conductivity (3) charge(2) resistance (4) power

• 2. How much current is drawn by a blender with a resistance of 40 Ω that is connected to a potential difference of 150 V?

• 3. How long does it take a total charge of 3.0 C to pass through a cross-sectional area of wire that carries a current of 23 A?