Current Electricity If you found electrostatics shocking you’ll find this revolting.

Voltage Voltage is the difference of electric potential between two points of an electrical or electronic circuit and is expressed in volts. Voltage is the difference of electric potential between two points of an electrical or electronic circuit and is expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor.

Voltage: Fluid Analogue In the reservoirs pictured, water flows due to a difference in the pressures of the two chambers In the reservoirs pictured, water flows due to a difference in the pressures of the two chambers Similarly, if there is a potential difference (voltage) across the different ends of a wire, charges will be pushed (flow) down the wire. Similarly, if there is a potential difference (voltage) across the different ends of a wire, charges will be pushed (flow) down the wire.

Electric Current Just as water current is flow of water molecules, electric current 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 Current Electric current (I) is rate at which charges flow through an area. SI unit: coulombs/second (C/s) or amperes (A) 1 A = 6.25  electrons/second

Voltage Sources and Currents Batteries & generators Batteries & generators Current will flow through a circuit if a voltage is applied across the circuit. Current will flow through a circuit if a voltage is applied across the circuit. Water will flow through a pipe if a pressure is applied across the pipe. Water will flow through a pipe if a pressure is applied across the pipe. Voltage causes current Voltage causes current

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

Electric Resistance Resistance is opposition to the flow of charge. Resistance is opposition to the flow of charge. It decreases the current. (Whereas voltage increases the current.) It decreases the current. (Whereas voltage increases the current.) Measured in Ohms (Ω) Measured in Ohms (Ω)

Resistance to Current Resistance is opposition to the flow of charge. SI unit: volts/ampere (V/A) or ohms (  ) Ohm’s Law :  V = IR Valid only for certain materials whose resistance is constant over a wide range of potential differences

Applications Resistors in a circuit can change the current. Resistors in a circuit can change the current. Variable resistors (potentiometers) are used in dimmer switches and volume controls. Variable resistors (potentiometers) are used in dimmer switches and volume controls. Resistors on circuit boards control the current to components. Resistors on circuit boards control the current to components. The human body’s resistance ranges from  (dry) to 100  (soaked with salt water). The human body’s resistance ranges from  (dry) to 100  (soaked with salt water). Currents under 0.01 A cause tingling. Currents under 0.01 A cause tingling. Currents greater than 0.07 A disrupt the heart’s electrical activity. Currents greater than 0.07 A disrupt the heart’s electrical activity.

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