First in come to me
•Come to me
•Quick quick...
•there’s prizes...
•And pixies...
•And other nice stuff...
•Not really but you do get to be in
charge of the game
Learning Objectives
21 November 2011
•‘Lost’ Energy
•To understand that energy is never
destroyed
•To be able to understand Sankey
Diagrams
•Key Words –
1.Sankey
Diagram
2.Energy
3.Transfer
4.Convert
Starter question
•How much energy efficient do
you think a car engine is?
•Guess how much of the chemical
energy is turned into kinetic
energy
5 Minute Task
Lesson Plan
•Learning Objectives
•What is efficiency?
•Calculation practice
•Sankey Diagrams
•Practice drawing a Sankey Diagram
•What is work? How do you calculate it?
•How does power relate to work?
Calculating efficiency
•Sounds scary, but really it is not!
•What do you think a really efficient
thing is? Tell your friend next to you.
•Getting a lot out of what you put in
is “high efficiency”
•Now sums
•Efficiency = Useful energy out
•
Energy in
Calculating
•An engine takes in 100 Joules of
energy but only 30 Joules of
movement is made.
•A light bulb takes in 50 J of
electrical energy but gives out 5 J of
light.
•An power station takes in 3 MJ of
chemical energy and makes 1 MJ of
electrical energy.
Sankey Diagrams
Energy
released
Heat
Elastic
Nuclear
Potential
...
...
...
Efficiency
Percentage Height or
of total
arrow in cm
500/2 000 (%) 25
2.5
0/2 000
0
0
Work and Power
•Read pages 56-59 in your Physics for
Cambridge IGCSE textbook
•Make notes on any key points
•Complete the questions on p 57 & 59
•Copy the equation for power and
substitute in the equation for work
•Read and attempt the exam-style
questions on pages 60-61.
Learning Outcomes
•All of you should …
– Know that energy is never lost and
understand where it goes and be able to
calculate work and power
•Most of you should…
– Be able to describe what work and
power are
•Some of you should…
– Be able to assess efficiencies, work
and power and make comments on them