Transcript Generating and Using Electricity

Generating and Using
Electricity
Direct Current and
Alternating Current
The current from a cell is called direct
current
The electrons only travel in one
direction in DC
Alternating current (AC) is when the
electrons move back and forth in a
circuit.
AC is the type of current that is
delivered to our homes and schools.
Advantages of AC
We can transmit extremely high voltage
electrical energy which saves on loss of
energy as heat.
Our homes use a lot less potential
difference than that which travels
through transmission tower wires.
In order to use this energy, we need to
change the size of potential difference
of the alternating current using a
transformer.
Transformers cannot work with direct
current.
The Meter
From a transformer, three wires go into our
homes.
Two are live and insulated carrying the
alternating current
The third is the ground which is neutral and not
insulated.
The meter registers the amount of energy that
is used in your home.
After passing through the meter, the electrical
supply is connected to a distribution panel.
The panel consists of either circuit breakers or
fuses for safety.
Safety
Ground fault circuit interrupter has a
small circuit breaker if there is any
difference in current between the right
and left slot. Used when near water.
Surge protector prevents damage to
circuits in electronic devices during
power surges caused by lightning.
Power Ratings
A factor that affects the amount of
electricity used in your home is the
power ratings of your appliances
Electrical Power is its rate of use of
electricity and is measured in
watts (W) or kilowatts (kW) which
is 1000 watts
Amount of Use
Electrical energy that is used is
calculated by multiplying the
power rating of an appliance by
the amount of time it is used for.
Measured in kilowatt hours (kWh)
The cost of electrical energy
depends on the amount of energy
used and the price per kWh.
Sample Problem
A hair dryer is rated at 1200W. It is used for 10
min each school day, when the cost of electrical
energy is $0.088/kWh. What is the cost of using
the hair dryer on all five school days during one
week.
Power = 1200W = 1.2 kW
Time= 10 min= 0.166h x 5 days= 0.833h
Energy used= Power x time
= 1.2kW x 0.83h
= 1.0 kWh
Rate = $0.088/kWh
Cost = energy use x rate
= 1.0 kWh X $0.088/kWh
= $0.088
You Try it!
P. 495 #1-5
Phantom Loads
The electricity that is used by an
appliance when it is turned off.
A stand-by mode
Something that is turned on by a
remote
Clock displays on microwave,
coffee maker, etc.
Efficiency
The ratio of useful energy output to total
energy input, expressed as a percentage.
Percent = useful energy output x 100%
efficiency
total energy input
You Try It!
P. 498 #1-4
P. 500 #1,2,4-6,8,9.