# KS4 Physics Energy in the Home.

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KS4 Physics Energy in the Home

Energy in the Home Uses of energy Heat loss and insulation
Contents Energy in the Home Uses of energy Heat loss and insulation Saving energy Summary activities

Energy in the home activity
How many different uses of energy can you spot? Teacher Notes Different uses of energy in the rooms of this home include: Bedroom (top left): ceiling light; radiator; lava lamp; laptop computer; bedside stereo/radio; hair dryer. Bathroom (top right): ceiling lights; electric shower; mirror light; electric toothbrush; hot water taps. Lounge (bottom left): ceiling light; radiator; mobile phone; television; DVD/video player; remote controls; open fire; radiator; lawnmower (in the garden outside the window). Kitchen (bottom right): ceiling light; fridge-freezer; microwave; food mixer; kettle; washing machine; boiler; cooker; radio.

Uses of energy What are four important uses of energy in our homes?
Heating Lighting Hot water Cooking Which one do you think we use the most energy for?

Uses of energy

Sources of energy in the home
The type of fuel we use to provide our energy at home will depend on many things but nearly all homes rely on a constant supply of electricity. Other fuels can be used for heating, hot water and cooking: oil gas coal What are some of the advantages and disadvantages of these forms of energy?

Comparing energy cost 60 260 210 250 MJ energy per £
Using the information in the table below, draw a bar graph that shows the amount of energy (in megajoules, MJ) per pound we get for each energy source. Put the energy sources along the x-axis, and the amount of energy per £ on the y-axis. 60 260 210 250 MJ energy per £ Electricity Gas Coal Oil

Comparing energy cost Energy (mJ) per £

Why do you think electricity is used so widely in homes?
Comparing energy cost What does the graph tell you? Electricity generation wastes energy and is expensive compared to the other fuels. Why do you think electricity is used so widely in homes?

Energy in the Home Uses of energy Heat loss and insulation
Contents Energy in the Home Uses of energy Heat loss and insulation Saving energy Summary activities

Heat loss from houses In houses, energy is lost from the roof, the door, the walls, the windows and the floors. Most energy is lost through the roof and walls. In order to reduce electricity bills and pollution, energy losses must be kept to a minimum.

Effect of insulation on heat loss

Reducing heat loss from houses
As you go through the next few slides complete the table below to show how various types of insulation prevent heat energy loss from our homes.

Reducing heat loss – curtains
Curtains reduce draughts (convection currents) leaving the house. They are opaque and so don’t allow much radiated heat to pass through them.

Reducing heat loss – walls
Most outside walls have an empty space between the two layers of bricks called a cavity. This reduces heat loss by conduction through the bricks. Cavity wall foam insulation is pumped in-between the bricks to prevent convection within the cavity. convection currents in the cavity foam prevents convection currents

Reducing heat loss – windows
A great deal of energy is lost through windows. By adding an extra pane, the trapped air between the two panes acts as an insulator and reduces heat loss by conduction. The insulating effect of the gap can be improved further by sucking all the air out to create a vacuum. Double glazing is expensive and difficult to smash without a special hammer.

Reducing heat loss – roof
The air heated by central heating is less dense than the cooler air around it. As a result, warm air rises. The ceilings become heated and eventually the heat escapes through the roof. Loft insulation contains trapped air, which forms an insulating layer between the loft and the rest of the house.

Radiators heat the wall a great deal – this wastes heat energy. Placing shiny silver-coated card between the wall and the radiator reduces heat loss by radiation by reflecting it back into the room.

Reducing heat loss – draughts
Draughts are convection currents. A great deal of heat energy is lost in this way but it is the easiest type of heat loss to prevent. Draught excluders are hairy or spongy strips that close gaps and prevent the convection currents escaping.

Insulation and heat loss

Insulation and heat transfer

The vacuum flask How does a vacuum flask keep hot drinks hot and cold drinks cold? 2. The plastic/cork lid is an insulator and prevents convection currents escaping. 1. The vacuum between the two layers of glass prevents heat leaving or entering by conduction. 3. The silvered walls prevent heat leaving or entering by radiation.

Energy in the Home Uses of energy Heat loss and insulation
Contents Energy in the Home Uses of energy Heat loss and insulation Saving energy Summary activities

payback time = cost to install
Payback time is how long it takes for the cost of installing insulation to be equalled by the savings from reduced energy costs. payback time = cost to install (years) saving each year For example: adding silver reflectors behind radiators costs £25 and saves £50 per year. Therefore, the payback time = 25/50 = 0.5 years or 6 months

Calculating payback time
What is the payback time for these types of insulation? 3 years 80 years 1 year 5 years Why is double glazing so popular if the payback time is so long?

Cost-effectiveness Cost-effectiveness is a comparison of how much insulation costs and how much it can save in reduced energy bills. Cost-effectiveness = saving each year cost to install For example: Adding silver reflectors behind radiators costs £25 and saves £50 per year. Adding draught excluders costs £50 and saves £50 per year. Cost-effectiveness = 50/25 Cost-effectiveness = 50/50 = 2 = 1 Therefore, reflectors are more cost-effective than draught excluders.

Calculating cost-effectiveness

Energy in the Home Uses of energy Heat loss and insulation
Contents Energy in the Home Uses of energy Heat loss and insulation Saving energy Summary activities

Glossary cavity wall – A wall constructed of two layers of bricks with a small air gap in between. This reduces heat loss by conduction. double glazing – Two panes of glass with a small air gap between them, which reduces heat loss by conduction. Sometimes the air is sucked out of the gap creating a vacuum. cost-effectiveness – A comparison of how much insulation costs and how much it can save in reduced energy bills. insulator – A material that is a very poor conductor of heat and so reduces heat loss. payback time – The time it takes for the cost of insulation to be equalled by the savings from reduced energy costs.

Anagrams

Multiple-choice quiz