Justify why an energy saving light bulb is

Justify why an energy saving light bulb is better for the environment than a regular one Start of lesson Level achieved: How to improve: Write your ideas in the first thought bubble!

Energy efficiency and Sankey diagrams

Objectives • To draw, and explain energy transfers from, Sankey diagrams • To distinguish between useful and wasted energy transfers • To calculate efficiency of different systems

Peer assess your partner’s work and suggest how they could improve grade criteria 8 • Everything for level 7 plus • Figures for efficiency of a normal vs energy saving light bulb • Several examples of the impact on the environment 7 • Detailed explanation of how energy saving light bulbs are more efficient • Diagram is correct and detailed • explanation of the resulting impact of this on the environment 6 • how energy saving light bulbs are more efficient • attempted a diagram • description of the resulting impact of this on the environment 5 • Short description of how energy saving light bulbs waste less energy than normal light bulbs

Present New Information • Whenever energy is transferred, some of it gets wasted. In other words some of the original energy is transferred to an unwanted form. • This can be illustrated using a SANKEY DIAGRAM

Sankey Diagram for a Light Bulb The total energy in = total energy out We represent amount of energy using the width of the arrow

Sankey Diagram for another Light Bulb In what way is this bulb different to the first one?

Apply to Demonstrate Draw a sankey diagram for the following: • A torch which uses 100 J of energy and gives out 20 J of light • A car engine takes in 100 k. J and gives out 40 k. J as kinetic, 40 k. J as heat, and 20 k. J as sound.

Review • Sankey diagrams show energy _____ • The useful energy goes _______ while the wasted energy goes _____ • The _______ of the arrows represent how much _______ is being transferred

Present new information Which light bulb is more efficient? How can you tell?

efficiency Efficiency is a measure of how much energy is useful, versus how much is wasted To calculate efficiency: efficiency = useful energy out total energy in Efficiency has no units, but can be made into a percentage (multiply answer by 100)

Construct your learning Around the room there are coloured post-it notes, each describing the energy transfers for the object which they are on. Your task: • Collect a post-it note • Identify the types of energy and if they are useful or wasted • Draw a sankey diagram of the transfers • Calculate the efficiency of the object Target level 6 a -7 c Target level 7 b -7 a Target level 8 c

Objectives • To draw, and explain energy transfers from, Sankey diagrams • To distinguish between useful and wasted energy transfers • To calculate efficiency of different systems

Review - Justify why an energy saving light bulb is better for the environment grade criteria 8 • Everything for level 7 plus • Figures for efficiency of a normal vs energy saving light bulb • Several examples of the impact on the environment 7 • Detailed explanation of how energy saving light bulbs are more efficient • Diagram is correct and detailed • explanation of the resulting impact of this on the environment 6 • how energy saving light bulbs are more efficient • attempted a diagram • description of the resulting impact of this on the environment 5 • Short description of how energy saving light bulbs waste less energy than normal light bulbs

Peer assess and justify their grade criteria 8 • Everything for level 7 plus • Figures for efficiency of a normal vs energy saving light bulb • Several examples of the impact on the environment 7 • Detailed explanation of how energy saving light bulbs are more efficient • Diagram is correct and detailed • explanation of the resulting impact of this on the environment 6 • how energy saving light bulbs are more efficient • attempted a diagram • description of the resulting impact of this on the environment 5 • Short description of how energy saving light bulbs waste less energy than normal light bulbs

Applying our knowledge We can calculate the efficiency of any system as long as we can measure the energy inputs and outputs. What will happen if we set up this circuit?

Useful formulae: V = IR Electrical power = VI = I 2 R = V 2/R Electrical energy = Power x Time = VIt = I 2 Rt = (V 2/R)t Heat energy = mass x specific heat capacity x temperature rise Total energy in = Useful energy out = Efficiency = m x C x θ Vx. Ixt

What do you think will make the most efficient heater?

Draw your results table • Change in temperature over ~5 minutes • You will need to also record: – Time – Voltage (average) – Current (average) – Mass of water used – Length and thickness of wire

Our experiment 1. Collect your equipment 2. Do pre-measurements (things that wont change throughout the experiment) 3. Set up the circuit 4. Get it checked 5. Start the experiment!

Group results Group 1 2 3 4 5 6 7 8 9 10 11 12 Length of wire Thickness of wire Average temp Efficiency of the rise (°C) heater

Review

Plenary • • What did you learn today? What did you find difficult? What do you feel most confident in? How do you feel now?