Chapter Twenty Electric Circuits 20 1 Charge 20

Chapter Twenty: Electric Circuits Ø 20. 1 Charge Ø 20. 2 Electric Circuits Ø 20. 3 Current and Voltage Ø 20. 4 Resistance and Ohm’s Law

20. 3 Current and voltage ØElectric current is measured in units called amperes, or amps (A) for short. ØOne amp is a flow of a certain quantity of electricity in one second. ØThe amount of electric current entering a circuit always equals the amount exiting the circuit.

20. 3 Voltage ØVoltage is a measure of electric potential energy, just like height is a measure of gravitational potential energy. ØVoltage is measured in volts (V). ØA voltage difference of 1 volt means 1 amp of current does 1 joule of work in 1 second.

20. 3 Voltage ØA difference in voltage provides the energy that causes current to flow.

20. 3 Voltage ØA useful meter is a multimeter, which Øcan measure voltage or current, and sometimes resistance. ØTo measure voltage, the meter’s probes are touched to two places in a circuit or across a battery.

20. 3 Batteries ØA battery uses stored chemical energy to create the voltage difference. ØThree 1. 5 -volt batteries can be stacked to make a total voltage of 4. 5 volts in a flashlight.

20. 3 Batteries ØA pump is like a battery because it brings water from a position of low energy to high energy.

20. 3 Measuring current Ø If you want to measure current you must force the current to pass through the meter. ØMultimeters can measure two types of current: alternating current (AC) and direct current (DC).

20. 3 Measuring current Ø Circuit breakers and fuses are two kinds of devices that protect circuits from too much current by making a break that stops the current.