Figure 2 CLOSING QUESTIONS 1. Do the cell emfs for the various metal combination

Question

Figure 2 CLOSING QUESTIONS 1. Do the cell emfs for the various metal combinations follow any mathematio pattern with respect to each other? Explain. 2. Do you expect measurements of potential made with a potentiometer to a gr with those made separately with an ordinary analog voltmeter? Why or why not? Which would give a more accurate value for a cell emf? Under what circumstances would an ordinary voltmeter give an accurate reading of cell emf (what would have to be true about the cel)? 3. Deduce the resistance of the spare ordinary voltmeter The Potentiometer 24.5

Explanation / Answer

1. cell emf's follow a simple mathematical combination rule wrt each other. The anode and cathode potential of any metal is already defined ( from its oxidation potential and its reduction potential) and physical addition of these gives us the EMF of the cell

2. as potentiometer measurement of voltage ensures there is no current in the device, thus ensuring any change to the circuit due to the instrument is avoided, it is the most accurate reading of voltage. An analogue voltge meter will give a close value but not accurate enough as there will be some current passing theough the voltmeter which will change properties of the circuit and hece giving us a different voltage readoing across the ptemeinals of the cell

3. let resistance of ordinary voltmeter be R

let the voltage of battery measured by potentiaometer method be E

let voltage measured by voltmeter be V

let internal resistance of the bettery be r

then

V = E - ir

and V = iR

i = V/R

V = E - Vr/R

Vr/R = E - V

R = Vr/(E - V)

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