Do this now! A (a)What are these diagrams called? (b)How efficient is each light bulb? B (c)Which is the energy-saving light bulb and which is the filament bulb?
Title: Efficiency Friction between the moving parts causes heating Use wider wires! Lubrication! The resistance of the wire causes it to get hot when current passes through Key Question: How can we improve the efficiency of Wall E? Air resistance causes energy to be lost to the surroundings Sound created when Wall E moves Streamlined Shape! Tighten bolts!
Like all machines, even when made more efficient, Wall E still loses heat to the surroundings. • Why is it classed as waste energy? Why is it so difficult to use? It heats up the surroundings, and spreads further and further away from the source.
Exam Style Question (about two topics) • The efficiency of a heating system in a house depends upon how much heat is lost. Explain why water pipes are often wrapped with the following material. (4) Foam (bubbles represent trapped air) Pipe Silver Foil
Mark Scheme • Silver foil causes any heat lost by radiation (1) to be reflected (1) back into the pipe. • Heat loss by conduction (1) is stopped through the foam because conduction cannot happen through the trapped air (1).
End of Chapter Questions • Only do 1,2,3 and 5. • Do not do 4 and 6. • We will finish off on Friday.