Chapter 7-2 Electric Current

Electric Pressure (Voltage) Charges flow from high-voltage areas to low-voltage areas Think about it like water: water flows from areas of high pressure to areas of low pressure Voltage difference = the push that causes electrons to flow Measured in volts (V)

Electric Current Flow of charges through a conductor Think of it as the number of electrons flowing through a wire (or molecules of water flowing through a pipe) Measured in amperes (A), commonly called “amps.”

What makes a battery work? 1.A chemical reaction inside the battery strips electrons off of atoms. 2.Electrons accumulate on the negative terminal. 3.If a conductor is connected to the (-) and (+) ends of the battery, electrons will flow. 4.At the positive terminal, electrons flow back into the carbon rod inside the battery. 5.The battery lasts as long as the chemical reaction inside can be sustained.

Dry-cell batteries Positive and negative terminals are separated by a paste, not a liquid.

Wet-cell batteries Positive and negative terminals are separated by a liquid (in this case, sulfuric acid).

What makes a light bulb glow? Resistance = tendency of a material to oppose the flow of electrons, measured in Ohms (Ω) copper wires = low resistance, no heat or light produced tungsten filament = high resistance, lots of heat and light produced

Is resistance good or bad? Low resistance is good for… wires that conduct electricity High resistance is good for… light bulbs space heaters electric blankets electric stoves resistors – protect delicate electronics from too much electric current passing through them

What affects resistance? Type of material Insulator = material with high resistance Conductor = material with low resistance Thickness of wire Thinner wire = higher resistance Temperature of wire Warmer temperature = higher resistance Length of wire Longer wires = higher resistance

Ohm’s Law If you increase the water pressure on a pipe, more water will flow through it. If you increase the voltage, more current will flow through it. If you put obstructions in the pipe, less water will flow through it. If you increase the resistance, less current will flow.

Ohm’s Law Voltage (V) Current (measured in amps) Resistance -- measured in Ohms (Ω)