9.2 The Power of Electricity (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 Power = the rate of change in energy measured as energy (joules) per second (J/s) 1 J/s = 1 watt (W) For example: a 25 W fluorescent bulb converts 25 joules of electrical energy every second into other forms See pages 320 - 324 (c) McGraw Hill Ryerson 2007

Calculating Power & Energy Consumption Power = Voltage x Current Energy = Power x Time

Paying for Electricity A Larger Unit for Energy Homes use LOTS of energy so bigger units are used. Instead of using watts, use kilowatts Instead of using seconds, use hours So, the power company keeps track of kilowatt•hours used. See page 325 (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 Converting Units Try: 525 W = ______________ kW 0.02 kW = _____________ W (c) McGraw Hill Ryerson 2007

Paying Your Power Bill The power company keeps track of your energy usage by reading your electric meter To bill you, the power company multiplies how much energy you have used by the cost per kW•h

(c) McGraw Hill Ryerson 2007 What is a kilowatt hour? (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007 For example: A 3 kW boiler runs for 30 minutes. How much does this cost if the utility company charges you$0.15/kWh? (c) McGraw Hill Ryerson 2007

Understanding Energy Use In most homes, electrical energy is measured by smart meters. Measures how electrical energy use changes in the home over the course of the day Information gathered is wireless sent Can track how and when electrical energy is used each day

(c) McGraw Hill Ryerson 2007 Energuide Labels Government of Canada requires all new electrical appliances be labeled Gives details about the amount of energy that an appliance uses in one year of normal use (c) McGraw Hill Ryerson 2007

ENERGY STAR® Labels Identifies a product as meeting or exceeding certain standards for energy efficiency

Phantom Loads Any device that consumes electricity when turned off but still plugged into an outlet. This wastes energy and cost money. Can account for approx. 900 kW•h of electrical energy use per year

(c) McGraw Hill Ryerson 2007 Examples: remote controlled devices computers washing machines microwave ovens (c) McGraw Hill Ryerson 2007