Mr' Perez

1
Mr. Perez

• Grade 6 Science
• Electric Power

2
Parallel Circuits Vs. Series Circuits

• Parallel Circuits
• Loads are connected in MORE THAN ONE PATH
• Each new path (with one load) that is added DOES
  NOT DECREASE the current
• Why? Each path will get the same voltage
• If more loads are added to one of the paths, the
  voltage to each bulb would decrease like a series
  circuit
• Why? Increased resistance in that path

• Series Circuits
• Loads are connected in ONE PATH
• Each added load that is connected DECREASES the
  current in the path
• Why? Because the resistance increases
• Ohms Law If the voltage (battery) doesnt
  change, and the resistance increases (added
  loads), the current decreases

3
What Is Electric Power?

• When you use any load, electrical energy is
  converted into other forms of energy
• Ex hair dryer (heat), lamp (light, heat)
• The rate at which electrical energy is converted
  into other forms of energy is called ELECTRIC
  POWER
• Electric Power can be calculated by using the
  following formula
• P I x V

4
Electric Power Equation

• Power (watts) Current (amps) x Voltage (volts)
• P I x V
• This equation means that the electric power is
  equal to the voltage (from a load in the circuit)
  times the current flow into that load
• In an electric appliance, or any electric
  circuit, the electric power that is used can be
  found by using this electric power equation
• You can use the following symbols
• Watts W Amps A Volts v

5
Solving Electric Power Problems
The batteries in a portable CD player provides
6.0 V. If the current in the CD player is O.5 A,
how much power does the CD player use?

• This is what you know
• This is what you need to find
• Solve the problem Write the formula and units

• voltage V 6.0 V
• current I 0.5 A
• Power P
• P I x V
• P 0.5 A x 6.0 V
• P 3 W

6
Protecting Electric Circuits

• As more and more devices are added to an electric
  circuit, the wires will begin to heat up
• When the wires get too hot from the added
  current, they overload the circuit
• Houses and buildings have circuit breakers and
  fuses to prevent this heat from the overload from
  causing a fire

7
Protecting Electric Circuits

• How do fuses and circuit breakers work?
• A piece of metal in the fuse melts and breaks,
  which stops the flow of electricity in the
  circuit
• A circuit breaker will trip or open like a
  switch when the circuit becomes overloaded
• This stoppage of electricity prevents a fire

8
The Cost of Using Electrical Energy

• Electric companies charge by the amount of
  electrical energy used, rather than by the
  electric power used.
• Electrical energy usually is measured in units of
  kilowatt hours (kWh)
• To convert watts to kilowatts
• Write a decimal after the number
• Move the decimal THREE PLACES to the LEFT
• Ex 2,221 W 2.221 kWh
• Ex 55 W 0. 055 kWh

9
The Cost of Using Electrical Energy

• The cost of using some household appliances is
  given in this table, where the cost per kWh is
  assumed to be 0.09/kWh
• Multiply the Energy Usage by the Cost
• Cost to use the stereo
• 0.09 x 0.27 0.02
• Cost to use the refrigerator
• 6.15 x 0.09 0.55