Electric Current sound/electricity.htm sound/electricity.htm

When you watch tv or use a computer, you rely on electrical energy to power them Electrical energy is the energy of electric charges Electric charges flow through wires The rate of flow of electric charges is called electric current Rate describes the amount of something over a period of time ex. Mph

How is Electric Current Measured?

Electric current describes the rate of flow of electrons through a wire Electric current is the amount of charge that passes a location in the wire every second Ex. Counting cars on a road over a period of time Electric current is expressed in units called amperes The symbol for ampere is A A wire with a current of 2 A has twice as much charge passing by each second as a wire with a current of 1 A

Direct Current

The two kinds of current are direct current (DC) and alternating current (AC) Both kinds of current carry electrical energy – they differ in the way the charges move Direct current - charges always flow in the same direction The electric current generated by a battery is DC – used by items such as flashlights, cars and cameras

Alternating Current

Alternating current – charges repeatedly shift from flowing in one direction to flowing in the reverse direction The current alternates direction The electric current from outlets are AC – most household appliances run on alternating current In the United States, the AC reverses direction and returns back to the original direction 60 times each second

Voltage

Voltage is the amount of work required to move each unit of charge between two points Voltage can be compared to the added pressure a full cup of water has on the flow of water compared to a cup with little water in it – voltage can be compared to the height of the water – the water flow can be compared to the flow of electric charge through the wire

Just as higher pressure produces a higher rate of water flow, higher voltage produces a higher rate of flow of electric charges in a wire Voltage is expressed in units of volts (V) Voltage is sometimes called electric potential because it is a measure of the electric potential energy per unit charge

Resistance

Some materials do not allow electric charge to move as freely as other materials The opposition to the flow of electric charge is called resistance Resistance is expressed in ohms (Ω) A higher resistance at the same voltage results in a lower current kpc kpc

Material Composition

A material’s composition affects its resistance Some metals, like silver and copper, have a low resistance and are very good conductors Some metals, like iron and nickel, have a higher resistance and are not as good at conducting electrical charge Electrical insulators, such as plastic, have such a high resistance that electric charges cannot flow through them Other factors that affect the resistance of a wire are thickness, length and temperature

A thin wire has a higher/lower resistance than a thicker wire A long wire has a higher/lower resistance than a shorter wire A hot wire has a higher/lower resistance than a cooler wire Conductors with low resistance are used for wire