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 PowerThe 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 PowerWe can measure the electrical power using

this equation:

Electrical power (watts)

Current (amps)

Voltage (volts)

Electrical energy usedKnowing 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 usedWe 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

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.

Electrical energy used

Cost of electricityOnce 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).