Current Current ElectricityElectricity

If you found electrostatics If you found electrostatics shocking you’ll find this shocking you’ll find this

revolting.revolting.

VoltageVoltage

VoltageVoltage is the difference of electric is the difference of electric potential between two points of an potential between two points of an electrical or electronic circuit and is electrical or electronic circuit and is expressed in volts. expressed in volts.

It is the measurement of the It is the measurement of the potential for an electric field to potential for an electric field to causecause an electric current in an an electric current in an electrical conductor.electrical conductor.

Voltage: Fluid AnalogueVoltage: Fluid Analogue In the reservoirs pictured, water flows due to a In the reservoirs pictured, water flows due to a

difference in the pressures of the two chambersdifference in the pressures of the two chambers Similarly, if there is a potential difference Similarly, if there is a potential difference

(voltage) across the different ends of a wire, (voltage) across the different ends of a wire, charges will be pushed (flow) down the wire.charges will be pushed (flow) down the wire.

Electric CurrentElectric CurrentJust as water current is flow of water molecules, Just as water current is flow of water molecules,

electric currentelectric current is the flow of electric charge. is the flow of electric charge.

Water (charge) continues to flow because a difference in pressure (voltage) is maintained with the pump. (similar to a battery or power supply)

Water (charge) flows from the reservoir of higher pressure (potential) to the reservoir of lower pressure (potential); flow stops when the pressure difference (potential difference) ceases.

Electric CurrentElectric Current Electric current (Electric current (II) is rate at which ) is rate at which

charges flow through an area.charges flow through an area. SI unit: coulombs/second (C/s) or SI unit: coulombs/second (C/s) or

amperes (A)amperes (A) 1 A = 6.25 1 A = 6.25 10 101818 electrons/second electrons/second

Voltage Sources and Voltage Sources and CurrentsCurrents

Batteries & generatorsBatteries & generators Current will flow through a circuit if a Current will flow through a circuit if a

voltage is applied across the circuit.voltage is applied across the circuit. Water will flow through a pipe if a pressure Water will flow through a pipe if a pressure

is applied across the pipe.is applied across the pipe. Voltage causes currentVoltage causes current

Classroom Practice Classroom Practice ProblemProblem

A typical 100 W light bulb has a A typical 100 W light bulb has a current of 0.83 A. How much current of 0.83 A. How much charge flows through the bulb charge flows through the bulb filament in 1.0 h? How many filament in 1.0 h? How many electrons would flow through in the electrons would flow through in the same time period?same time period?

Electric ResistanceElectric Resistance

Resistance is opposition to the flow Resistance is opposition to the flow of charge.of charge.

It decreases the current. (Whereas It decreases the current. (Whereas voltage increases the current.)voltage increases the current.)

Measured in Ohms (Measured in Ohms (ΩΩ))

Resistance to CurrentResistance to Current Resistance is opposition to the flow of charge.Resistance is opposition to the flow of charge.

SI unit: volts/ampere (V/A) or ohms (SI unit: volts/ampere (V/A) or ohms ())

Ohm’s Law : Ohm’s Law : VV = = IRIR Valid only for certain materials whose resistance is Valid only for certain materials whose resistance is

constant over a wide range of potential differences constant over a wide range of potential differences

ApplicationsApplications Resistors in a circuit can change the Resistors in a circuit can change the

current.current. Variable resistors (potentiometers) are used in Variable resistors (potentiometers) are used in

dimmer switches and volume controls.dimmer switches and volume controls. Resistors on circuit boards control the current Resistors on circuit boards control the current

to components.to components. The human body’s resistance ranges from The human body’s resistance ranges from

500 000 500 000 (dry) to 100 (dry) to 100 (soaked with salt (soaked with salt water).water). Currents under 0.01 A cause tingling.Currents under 0.01 A cause tingling. Currents greater than 0.07 A disrupt the Currents greater than 0.07 A disrupt the

heart’s electrical activity.heart’s electrical activity.

Classroom Practice Classroom Practice ProblemsProblems

A typical 100 W light bulb has a A typical 100 W light bulb has a current of 0.83 A. If this bulb is current of 0.83 A. If this bulb is connected across a 120 V potential connected across a 120 V potential difference. Find the resistance of the difference. Find the resistance of the bulb.bulb.