Do Now (10/10/13):

• What do Watts measure?

• Where do you see labels in Watts?

Electrical Power

Questions to ponder

• What is electrical power?

• How do you calculate energy?

• How do you calculate cost of electricity?

Calculating Cost of Power

• Cost is calculated as the amount per Kilowatt hour

• Common cost is usually about $0.08 -$0.11 per kilowatt hour.

• Calculations are made by multiplying the cost by the usage in kilowatt hours.

What is electrical power?

• Electric Power , P , is the rate at which electrical energy is converted into other forms of energy

• Unit for power : Watt(W)

• 1 kW = 1000 W

How do you calculate energy?

Power

Energy

Time

Energy= Power x time

How do you calculate energy?

• If it takes 300 W kettle 30 minutes to boil the water,

(a) what is the electrical energy used in kWh?

How do you calculate energy?

• Calculate energy in kWh

• To find energy in kWh, the power must be in kWkW and timetime must be in hr.

• 1 000 W = 1 kW!!!!• Energy (kWh) = Power(kW) x time(hr)

= 300/1000 x 30/60

= 0.15 kWh

It takes 300 W kettle 30 minutes to boil the water.

How do you calculate the cost of electricity?

• Step 1 : Calculate the electrical energy in kWh

• Step 2 : Find the cost of electricity.

Electrical energy is sold in kWh

For example , each unit costs 20 cents. This means each kWh costs 20 cents

How do you calculate the cost of electricity?

• Calculate cost of electricity

• Step 1 : Calculate energy in kWh.

Energy (kWh) = Power(kW) x time(hr) = 300/1000 x 30/60 = 0.15 kWh

• Step 2: Calculate costTotal cost = Energy (kWh) x cost per unit = 0.15 x 20 = 3 cents

It takes 300 W kettle 30 minutes to boil the water. Calculate the cost if each units costs 20 cents.