Have you ever been told to turn off the lights in your room when you leave? This is because energy costs money. used by our lights and appliances.

The cost of electricity varies. For simplicity sake assume that

electricity costs 8¢/kW•h.This means that if a 1000 W appliance is left on for 1 h, it uses 8¢ worth of electricity.

1. A 100 W light bulb is left on from 10:00 at night to 7:00 the next morning.

2. A turkey takes 3 h to cook in a 1500 W oven.

3. You watch a 500 W television set for 7 h.

Start by drawing your floor plan Put on large appliances – Stove, Fridge,

TV, Freezers Add secondary appliances, computers,

fish tanks, toasters, and blenders Finally put on lights You need to think of how many hours

the appliance runs per day (3hrs per day x 30 days in a month)

Start calculating your power 1000W = 1KW then 1KW x 8cents = cost

How many KW/hour you use per month Cost of your power bill is KW/hr x 8cents Add Delivery charges of 90% of total

electrical cost Add Administration fee of 7%

The Ray Model of Light

The ray model of light helps you to predict where shadows will form and how large they will be

• Light travels in straight lines• Objects farther away from the light source cast a

smaller shadow and objects closer to the light cast a larger shadow

• Try shining a light source at a piece of glass, a sheet of white paper and a sheet of construction paper. Identify which object is transparent, translucent and opaque. Draw the ray diagram for each object.