Current Electricity

Comparing Electricity Static electricity is a build up of electrons This creates attractions and repulsions The electrons are held in place until there is a discharge, then the electrons move from one place to another The movement of electrons is current electricity!!

Flowing electrons is current Current electricity can be AC (alternating current) like wall outlets and ceiling lights Current electricity can be DC (direct current) like a bolt of lightning or from a battery In both cases, electrons are moving from the negative end (more electrons) to the positive end

Four Terms Four major terms associated with current electricity are Voltage (potential difference) is the pressure on the electrons to make them move Current is the amount of electrons moving Resistance is the push against the movement of the electrons Power is the work being done by the moving electrons in a given time

Think about electricity like a big bucket of water The more full the bucket, the harder the water pushes out the faucet – this push is voltage The more the faucet is opened, more water flows out – this flow of water is current

The faucet can be opened all the way and make it easy for water to flow, or it can be closed part way and make it harder for water to flow The “harder to flow” is resistance to flow of water – it also is the resistance to flow of electricity

The water coming out of the faucet can spray, wash away dirt, even turn a water wheel to make electricity All of these things are work Measuring how much work is done in a specific amount of time is power Electrical power is watts

Conductors are materials that allow electricity to flow through them Good conductors, like copper wire, have low resistance. This means that they will easily allow electricity to pass through them Conductors conduct because they hold electrons loosely, and electrons can pass from one atom to the next, and down through the whole piece of material

Insulators are materials the do not allow electricity to pass through them Insulators hold their electrons tightly, so they can not be passed or moved

Voltage Sources Electricity coming from a battery flows from the negative terminal to the positive terminal. It flows directly from one to the other, in only one direction. Wall outlets have electricity that keeps changing, or alternating direction. This means that the electricity is moving forward through the wire, then back, then forward again This back and forth motion of electrons can still do work, just as the back and forth motion of a saw still cuts

Ohm’s Law There is a relationship between voltage, current, and resistance Think back about the water tank If there is not much water in the tank, there will not be much current – regardless of how much the faucet is opened. If there is a lot of water in the tank, the faucet controls how much water flows out. The more resistance there is, the less current

Ohm’s Law Formula Voltage = current * resistance Or Current = voltage / resistance Hopefully this makes sense – if the resistance increases, the current decreases!! The formula is written V=IR V = voltage I = current R = resistance

Taking the measure Voltage or Potential Difference is measured in Volts (V) Current is measured in amperes or amps (I) Resistance is measured in ohms(R) Power is measured in watts(P)

Practice What is the current of a 9 volt circuit with 20 ohms of resistance? V=IR, or I=V/R I=9 v/20 ohms I=.45 amps

What is the voltage of a circuit with 50 ohms of resistance and.01 amps? V=IR V=.01 amps * 50 ohms V=.5 volts

What is the resistance of a 110 volt circuit with 4 amps of current? V=IR, or R=V/I R=110 v/4 amps R= 27.5 ohms

Practice What is the voltage of a circuit with 10 ohms of resistance and 15 amps of current? V=IR I=15 amps R= 10 ohms V = 15 amps * 10 ohms V = 150 volts

Practice What is the resistance of a 25 volt circuit with 5 amps of current? R = V/I V= 25 Volts I= 5 amps R = 25 Volts/5 amps R = 5 ohms

Power Power is volts times amps P=VI

Practice What is the power of a 5 volt circuit with 15 amps of current? P=VI P= 5 volts * 15 amps P= 75 watts