EMPA Information

Provisional Dates:-

Weds 5th May – Practical (Section A) – All Day (no time limit) consists of two tasks.

Fri 7th May – Written Paper (Section B) 1hr 1/4.

Remember Unit 1 exam is on Thursday 27th May.

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.)

Resistor Rules

Electricity Lesson 8

Learning Objectives

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

Recap

What are the circuit rules for current and potential difference?

Potential Difference Rule 1

321 VVVV

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:-

321 VVVV

11 IRV 22 IRV 33 IRV

Resistors in Series

The resistance across all three resistors is:-

Then cancelling the Is on the right hand side:-

I

IRIRIR

I

VR 321

321 RRRR

Quick Question

(a) What is total resistance of the three resistors connected in series?

Resistors in Parallel

Resistors in Parallel

The current splits at a junction but the potential difference is the same across both:-

Using R=V/I we can say:-

21 III 21 VVV

11 R

VI

22 R

VI

R

VI

Resistors in Parallel

So it follows that:-

Dividing throughout by V gives:-

21 R

V

R

V

R

V

21

111

RRR

Resistors in Parallel What is the

resistance across the two resistors if R1 = 10 Ω?

R2 = 5 Ω?

If it is a 1.5 V cell evaluate I, I1 and I2?

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?