1. Lecture 54 – Lecture 55 Electric Power Ozgur Unal
NIS – PHYSICAL SCIENCE
Lecture 54 – Lecture 55
Electric Power
Ozgur Unal

2. Series and Parallel Circuits
A circuit is a closed path that electric current flows.
There are two kinds of circuits: Series Circuits and Parallel Circuits
Series Circuits:
In a series circuit, the current has only one loop to flow through.
Series circuits are used in flashlights and
some holiday lights (christmas trees).

3. Series and Parallel Circuits
In a series circuits, if one of the components is broken, the current cannot flow  Open circuit
Example: A burned-out light bullb
causes an open circuit.
Parallel Circuits:
Parallel circuits contain two or more
branches for current to move through.

4. Series and Parallel Circuits
Consider the parallel circuit shown below.
Which branch has higher current
flowing through?
Which branch has lower current
Check out Figure 18!!
What kind of circuit should be used to wire houses?

5. Household Circuits
In a house many appliances draw current from the same circuit: More appliances  more current through the wires
As the amount of current increases, so does the amount of heat produced in the wires  insulation may melt and bare wires can cause a fire!
To protect against overheating of the wires, all household circuits contain either a fuse or a circuit breaker.
A fuse contains a small piece of metal that melts if the current becomes too high  open circuit results
A circuit breaker contains a piece of metal that bends when the current is too large  open circuit results

6. Electrical Power
Electrical energy can be converted to other types of energies.
Example: A fan converts electrical energy to mechanical energy
A light bulb converts electrical energy to light and thermal energies.
The rate at which electrical energy is converted to another form of energy is the electrical power.
Electrical Power = Current x Voltage Difference
(Watts) = (Amperes) x (Volts)
P = I * V
Example: A toaster oven is plugged into an outlet that provides a voltage difference of 120 V. What power does the oven use if the current is 10 A?

7. Electrical Energy = Electrical Power x Time
Electrical energy consumed by an electrical device can be calculated using its power.
Electrical Energy = Electrical Power x Time
kWh = kW x hours
E = P * t
Example: A refrigerator operates on average for 10 h a day. If the power of the refrigerator is 700 W, how much electrical energy does the refrigerator use in one day?
Example: Calculate the monthly cost of using this refrigerator if the cost per kWh is 0.09 $.