Potentiometer/Galvanometer problem

1. Mar 9, 2010

thelibertine1

1. The problem statement, all variables and given/known data

In the above (attached) potentiometer circuit the total range of the potential that can be measured by the 800ohm resistance AB is 1.6V. The resistance, R, of the meter G is 84 ohms. The slider is set at X to balance a potential E of 1.4000V.

a) What is the resistance included between X and B?
b) If the value of E is actually 1.4014V, what current will flow through the meter?
c) There are available other meters whose resistances,R, are different from that of the 84 ohm one, but which have the same senstivity for the same power supplied to them. What would be the optimum resistance which such a meter should have to make the above measurement(ie: what is the condition for maximum power transfer to the galvanometer?)

2. Relevant equations
V = IR

3. The attempt at a solution
The voltage between A and X is R1, X to B is R2
a)
I = the voltage across A to X / R1 + R2
I = 2/800 = 2.5E-3 A
voltage across R2 is then equal to voltage E ?
so R2 = V/I = 1.4 / 2.5E-3 = 560 ohms
Is this correct?

b) Not sure what they are asking to do. Not quite sure how the whole circuit works, is the current through G 0 in the first question? And is it not anymore? Why is the initial conditions important (the total range of potential) ?

c) Not sure where to start :S

Any help is really appreciated. Thanks.

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