1. EMPA Information Provisional Dates:- Weds 5 th May – Practical (Section A) – All Day (no time limit) consists of two tasks. Fri 7 th May – Written Paper (Section B) 1hr 1/4. Remember Unit 1 exam is on Thursday 27 th May.

2. EMPA Practice Next week in Friday P1 with Dr. Poulton. Following week on Thursday P1 (BK) +P2 (CJP). More will follow...Don’t Panic! I can do more in Phys. Workshop (need advance warning.)

3. Resistor Rules Electricity Lesson 8

4. Learning Objectives To know and derive the rules for resistors in series and parallel.

5. Recap What are the circuit rules for current and potential difference?

6. Potential Difference Rule 1

7. Resistors in Series The pd across all the components is equal to the sum of the pds across each component:- Using R=V/I, we can write:-

8. Resistors in Series The resistance across all three resistors is:- Then cancelling the Is on the right hand side:-

9. Quick Question (a) What is total resistance of the three resistors connected in series?

10. Resistors in Parallel

11. The current splits at a junction but the potential difference is the same across both:- Using R=V/I we can say:-

12. Resistors in Parallel So it follows that:- Dividing throughout by V gives:-

13. Resistors in Parallel What is the resistance across the two resistors if R 1 = 10 Ω? R 2 = 5 Ω? If it is a 1.5 V cell evaluate I, I 1 and I 2 ?

14. Practice Calculation What is the resistance across the 4 ohm and 8 ohm resistors? What is the total resistance? What is the current in each part of the circuit?