V A +- V A +- Which is the correct way to measure current and voltage? Use if low resistance Use if high resistance Good ammeters have low resistance Good voltmeters high resistance

V 400  800  What will be the potential difference on the voltmeter? 12V Using a Wheatstone Bridge means you don’t need an accurate (expensive ) voltmeter or ammeter.

V X k  15 k  30 k  75 k  V R1R1 R2R2 R3R3 R4R4 Wheatstone Bridge When bridge is balanced ( meter reads zero) 12V Tutorial Questions 25 to 27

V R1R1 R2R2 R3R3 R4R4 Find the resistance of A,B and C Discuss - choice of R 1 and R 2. - the resistor in series with the meter. - why a shunt is used. A is between 100  and 400  B is over 10 k  C is less than 10 . Tutorial questions 28 to 30 Experiment

Using an out of balanced Wheatstone Bridge 1.Adjust the bridge so it is balanced at the required temperature eg 20 o C 2.Plot a graph of R and voltage. 3.Calibrate this graph to give temperature. V R V 0 Tutorial questions up to and including 32 SAQs to page 27 end of booklet