Download cost_of_electricity

True or False?
• The voltage in a parallel circuit is the
same across each parallel branch.
• In a parallel circuit the combined
resistance is greater than the
resistance in the parallel branches.
• In a series circuit the equivalent
resistance is less than the sum of
resistances of the components.
True or False?
• The units for E.M.F. can be written as
amps/ohms.
• The higher the resistance the higher
the current.
• The current through a LDR increases
when it is brighter.
I’ve got the power
• Electrical power
• Electrical energy used by an appliance
• Cost of electrical energy used
Electrical Power
The electrical power of an appliance is a
measure of how quickly that appliance
transfers electrical energy and it is
measured in watts (W), or kilowatts (kW).
1000W = 1kW
Electrical Power
We can measure the electrical power using
this equation:
Electrical power
(watts)
Voltage
(volts)
Current
(amps)
Electrical energy used
Knowing that the power is the rate at which
the appliance transfers energy, we can say
that the electrical energy used by the
appliance depends on:
• How long the appliance is used for (time)
• How quickly the appliance transfers
energy (its power)
Electrical energy used
We can count the units of electrical energy
used by using the following equation:
Number of units used = power x time
(kWh)
(kW)
(h)
Where the number of units used is
measured in kilowatt-hour
Electrical energy used
Click on the right ending.
As power is the rate of energy transferred…
1. …the number of units used is a form of power.
2. …the number of units used is voltage divided by current.
3. …the number of units used is a measure of energy.
4. …the number of units used is the cost of the energy used.
Cost of electricity
Once we know the amount of energy used for a
certain number of hours (i.e. the number of
units used), we can work out the cost of the
electrical energy used by the appliance, if we
know the cost per unit.
Cost = Number of units used x cost per unit
The cost per unit is normally given in pence (p).