ELECTRICAL ENERGYChapter 13

Section 3

SERIES CIRCUIT

• A series circuit is a circuit that has only one loop for the current to flow through• Series circuits are used in flashlight and some Christmas lights• If any part of the circuit is disconnected, the whole circuit is open• When on light goes out, they all go out.

• The current is the same throughout the entire circuit• The total resistance in the circuit is equal to the sum of the individual resistances.

PARALLEL CIRCUITS

• When you shut of one light in your house, do all the lights go out?• No…because houses are wired as

parallel circuits not series circuits

• Parallel circuits contain two or more branches for current to travel through

• The total current in the circuit equals the sum of the currents in its parallel branches.• More current will travel through

the branches with the least amount of resistance

CIRCUIT DIAGRAMS

• Electric circuits, whether simple or complex, can be described in a variety of ways

• An easy way to visualize a circuit is by drawing a circuit diagram

• There are common symbols used to represent parts of a circuit

LET’S TRY ONE…

AN ANOTHER ONE…

HOUSEHOLD CIRCUITS

• Household circuits are mostly a combination of parallel circuits

• The voltage difference is supplied by the generator at a power plant

• In the US, the voltage difference is typically 120V

• Some appliance require more voltage difference (240V)• Dryers• Stoves

• As current increases, thermal energy increases

• How do we protect you home from too much thermal energy• Coated wires• Fuses• Circuit breakers

FUSES AND CIRCUIT BREAKERS

Fuses

• The fuse is part of the circuit

• Contain a small piece of metal that melts if the temperature gets too high

• The metal melting breaks the circuit

• Must be replaced

Circuit Breakers

• Part of the circuit

• Contains a piece of metal that bends when the current is large and too hot

• Circuit breakers can be reset

ELECTRICAL POWER

• Electrical energy is being converted to many different types of energy• Fan

• Electricalmechanical• Hair dryer

• Electricalthermal• Light bulb

• Electricallight

• The rate at which electrical energy is converted to another form of energy is electrical power

ELECTRICAL POWER

• The electrical power used depends on the voltage difference and the current

Electrical power = current x voltage difference

P = I x V

• Electrical power is often expressed in kW

LET’S TRY ONE…

• The current in an electric clothes dryer is 15 A when it is plugged into a 240V outlet. How much power does the clothes dryer use?

3.6 kW

ANOTHER ONE…

• A flashlight bulb uses 2.4 W of power when the current in the bulb is 08 A. What is the voltage difference?

3V

ELECTRICAL ENERGY

• Power companies charge by the amount of electrical energy used rather than the electrical power used

• Electrical energy is measures in units called kilowatt hours (kWh)

Electrical energy = electrical power x time

E = P x t

EXAMPLE 1

• A microwave oven with a power rating of 1200 W is used for 0.25 h. How much electrical energy is used by the microwave oven?

• 0.30 kWh

THE COST OF ELECTRICAL ENERGY

• To determine the cost of electricity you need to calculate the amount of electrical energy used by the energy rate charged by the power company.

• For example, if a 100 W lightbulb is left on for 5 hours, what is the cost of the electricity if the company charges $0.10 per kWh?• First calculate the energy used

• Then calculate the cost

• $0.05

EXAMPLE 2

• A TV with a power rating of 200 W uses 0.8 kWh in one day. How many hours was the TV used that day?

• 4 hours