1. Electrical potential energy and resistance

2. review Last class we discussed charge and current
Charge (q) is a measure of the excess or deficit of electrons and is measured in Coulombs. Where Coulomb equals 6.24 x electrons
Current (I)is a measurement of how quickly electrons travel through a circuit. It is measured in Amperes. Where 1 ampere is equal to 1 C/s passing a point on the circuit.

3. Water Wheel Analogy
A simple electric circuit can be viewed as a system of pipes that channel water around using a pump in order to make a wheel spin

4. Getting Energy for a circuit
Water is pumped up to give it the ability to fall on the wheel with a lot of energy and make it spin. The higher the water is pumped, the more energy it will have and the faster the wheel will spin

5. electricity
In an electrical circuit, the battery is the pump and the electrons are the water. The battery releases the electrons into the circuit and gives them energy

6. Electrical Potential Energy
As the water falls and moves the water wheel it loses energy
Same thing with
electrons. The load
provides resistance
and the resistance
takes potential
energy away from the electrons. When electrons
return to the battery, they have lost all of their
energy. The battery then re-energizes the electrons
and sends them back into the wires.

7. Electric Potential
This potential energy that the battery gives the electrons is called the voltage (V).

8. Resistance
The greater the voltage, the greater the current. In other words, the more energy the electrons receive from the battery, the faster they will move through the circuit.
But there is one more factor; resistance
Resistance impedes, or slows down the flow of electrons. Wires are made of copper wire which conducts electricity well and provides virtually no resistance.
But loads, like light bulbs, provide more resistance and take some of the energy from the electrons. This causes the current to decrease.

9. Resistance
There are three things that affect resistance in an object. They are:
The material – Insulators provide more resistance than conductors
The cross sectional area
The length
Long thin loads provide
more resistance than
short wide loads

10. Voltage, Current & resistance
There appears to be a fixed relationship between the three variables
That relationship is V = IR or
Voltage = Current x Resistance

11. V = IR
That means that current and resistance are inversely related. That means that as resistance increases, current decreases by the same proportion.
This formula holds true for the entire circuit and for each individual load

12. Learning Check
The following electric circuit is powered by a 20 V power source (battery). The resistance provided by the light bulb is 5 ohms ( ). What is the current of the circuit?

13. Learning check Simple!! Since V = IR I = V/R
So, substituting I = 20/5 = 4 Amperes
or 4 Coulombs per second

14. Series vs Parallel
In circuits that have several loads, the value of one of the variables (i.e. voltage, current or resistance) at one point in the circuit could be different than at another point.
The next slide shows how
the variables for the entire
circuit compare to the
values at a single load
based on the type of
circuit

15. Series vs parallel VT = V1 + V2 + V3 IT = I1 = I2 = I3
RT = R1 + R2 + R3
VT = V1 = V2 = V3
IT = I1 + I2 + I3
1/RT = 1/R1+1/R2 +1/R3