Power Electrical Energy and Efficiency 1 Power 2

KEY TERM - POWER Recall: Sports Venue example for Current and Voltage �Now that

Electrical Power (P) �The rate at which electrical energy is used = Current (the

Typical Power Ratings of Appliances �Clock = 0. 0050 k. W �Clothes dryer =

Electrical Energy �The amount of electrical energy used is calculated by multiplying the number

Cost of Electrical Energy �The cost depends on the amount of energy used and

Step 1 – Convert 1200 W k. W Given xk. W 1200 W W

Step 2 – Find the time used in hours xh =1 h xh 10

Step 3 – Calculate Energy Used = power (k. W) x time (h) =

Step 4 – Calculate Cost = energy used x rate =

Step 4 – Calculate Cost = energy used x rate = 1. 0 k.

Electrical Efficiency �How efficient a device is tells us how much energy it produces

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Power, Electrical Energy and Efficiency 1. Power 2. Electrical Energy 3. Energy Costs 4. Calculations 5. Efficiency

KEY TERM - POWER Recall: Sports Venue example for Current and Voltage �Now that we’ve found the components which determine how much the venue will make, how do we calculate their total profit? �We need to take the number of people who came and multiply that number by the price per ticket. �This is the same for Electrical Power which is measured in Watts

Electrical Power (P) �The rate at which electrical energy is used = Current (the number of electrons passing by the point) X Voltage (how much energy they give up) ◦ P=IXV Measured in Watts (W) � 1000 W = 1 k. W �We mostly use k. W

Typical Power Ratings of Appliances �Clock = 0. 0050 k. W �Clothes dryer = ____ �Washing Machine = 0. 5 k. W �Computer with monitor and printer = ____ �LCD TV = ____ �Video game console = ____ �Dishwasher = ____ �Fridge / Freezer = ____ �Home Air Conditioner = ____ �Ceiling Fan = ____

Typical Power Ratings of Appliances �Clock = 0. 0050 k. W �Clothes dryer = 4. 0 k. W �Washing Machine = 0. 5 k. W �Computer with monitor and printer = 0. 20 k. W �LCD TV = 0. 12 k. W �Video game console = 0. 10 k. W �Dishwasher = 1. 3 k. W �Fridge / Freezer = 0. 5 k. W �Home Air Conditioner = 1. 0 k. W �Ceiling Fan = 0. 025 k. W

Electrical Energy �The amount of electrical energy used is calculated by multiplying the number of k. W X time (hours) �All household appliances must have an Ener. Guide label which shows how much energy the appliance uses in one year and also gives the energy use per hour (k. Wh) �The higher the energy use, the more expensive it will be to run it!

Cost of Electrical Energy �The cost depends on the amount of energy used and the price that is charged for it. �To calculate cost you multiply the amount of energy used (k. Wh) by the price (¢/k. Wh). �E. g. Solve the following problem

Step 1 – Convert 1200 W k. W

Step 1 – Convert 1200 W k. W Given xk. W 1200 W W Conversion = 1 k. W xk. W = 1 k. W x 1200 W 1000 xk. W = 1. 2 k. W

Step 2 – Find the time used in hours

Step 2 – Find the time used in hours xh =1 h xh 10 min 60 min xh = 0. 1666 h /day x 5 days = 0. 83 h =1 hx 60 min

Step 3 – Calculate Energy Used = power (k. W) x time (h) = =

Step 3 – Calculate Energy Used = power (k. W) x time (h) = 1. 2 k. W x 0. 83 h = 1. 0 k. Wh

Step 4 – Calculate Cost = energy used x rate =

Step 4 – Calculate Cost = energy used x rate = 1. 0 k. Wh x 8. 8¢ k. Wh = 8. 8 ¢

Electrical Efficiency �How efficient a device is tells us how much energy it produces compared to how much it consumes. �I. e. A light bulb requires 200 J of energy to light up but only produces 100 J of light energy. Calculate the efficiency of the light bulb. Given: Energy In = 200 J, Energy (light) Out = 100 J % efficiency = Energy Out / Energy In X 100 % % efficiency = 100 J / 200 J X 100 % = 50 % The efficiency of the light bulb is 50 %. That means that 50 % of the energy is converted into light, the remainder is converted to and lost as heat.