Potential Difference Objectives 03 December 2018 Potential Difference What do I know already? How can we charge something with Static? How does electric current flow in a wire? What is the difference between an electrical conductor and an insulator? What is work done? What are the units of charge? Rub two insulators together. Flow of delocalised electrons. A conductor lets current flow and an insulator doesn’t. Work done = Energy Transferred. Charge is measured in Coulombs. Objectives Be able to describe what potential difference in an electrical circuit is. HSW: AF1 – Thinking Scientifically – Using and evaluating models to describe abstract ideas. Used before in: Science A Will use again in: lesson 4 - circuits PLTS: Team workers – Work collaboratively with others. Used before in: lesson 2 – static to current Keywords Current, Amp, Charge, Coulomb, electron, insulator, conductor, energy, Potential Difference, Voltage, Volts.

OUTCOMES All students should know the units for Potential Difference, Work Done and Charge and know how electrical energy flows in circuits. Most students should be able to define what Potential Difference is use the equation: PD = Work / Charge and be able to describe the difference between electron flow and conventional current. Some students should be able to remember and rearrange the equation: PD = Work / Charge.

Circuit Demo Your teacher will demonstrate a circuit to you. What happens when more cells are added? What happens when more load is added? What is electric current? What is potential difference? Which direction do the electrons go? What is conventional current?

Conventional Current

Potential Difference – Student Model You will now be the charge in a circuit. 1) Describe the model – what did we do? What is the charge, the cell, the load? How are differences in potential energy shown? 2) What are the good things about the model? 3) What are the things that we can improve?

Potential Difference – Explanation PD - + 0J 1J 1J Charge moves from negative to positive The E.M.F of the power supply tells us how much energy is transferred to each 1 C of charge. Each charge then transfers this much energy to the components in the circuit. + - 1J 0J 0J

Potential Difference – Water Model Describe the model – what is the charge, the cell, the load, how are differences in potential energy shown? 2) What are the good things about the model? 3) What are the things that we can improve? 4) Is this a better model than our student model or not? Explain Why/Why Not.

Demonstrate your understanding Do the questions from the worksheet – they have been rated for difficulty. If you finish – try these A* questions: 7a) Explain in terms of the energy per charge, what would happen to the loudness of a series of buzzers as you added them one by one into a circuit containing a constant power source. 7b) A teacher models potential difference by asking students to stand in a circle. He passes the first student ping pong balls and asks them to keep passing pass them around the circle. The last student in the line throws the balls around the class. In this model, (i) What are the ping pong balls? (ii) What are the students? (iii) What is the teacher? (iv) Evaluate this model by describing the positive and negative things about it.

Compare your answers Compare your answers to questions 1-5, see if you can get an answer for each one. We will go through 6 and 7 as a class.

a) V = 1000 mV = ______ V W = ? Q = 20 C b) V = ? W = 1.25 kJ To do these hard questions – read the question carefully, rearrange equations and convert into the simplest units. 6. Find the unknown quantity (CONVERT FIRST to volts, joules, or coulombs) a) V = 1000 mV = ______ V W = ? Q = 20 C   b) V = ? W = 1.25 kJ = _________ J Q = 1500 C c) V = 1.21 GV =_________V Q = 2 000 000 C

To improve your grade - be able to evaluate models and justify your reasoning – Your teacher will demo these and discuss the answers. 7a) Explain in terms of the energy per charge, what happens to the loudness of a series of buzzers as you added them one by one into a circuit containing a constant power source. 7b) A teacher models potential difference by asking students to stand in a circle. He passes the first student ping pong balls and asks them to keep passing pass them around the circle. The last student in the line throws the balls around the class. In this model, (i) What are the ping pong balls? (ii) What are the students? (iii) What is the teacher? (iv) Evaluate this model by describing the positive and negative things about it.

Tell me two things... (for each) that you have done well this session that you know now that you didn’t know at the start that you could do better next time that you would like to know more about 2

Hotseat/Outcomes Quiz What are the units for Potential Difference? What are the units for Work Done? What are the units for Charge? How does energy flow around electrical circuits? Define Potential Difference What is the difference between electron flow and conventional current. In terms of Potential Difference and Charge, what is Work done? Work done = …