In a potentiometer, why is it necessaryto i) use a long wire ii) have uniform area of cross section of the wire and iii) use a driving cell whose emfis taken to be greater than the emfs of the primary cells?
Answers
(1)long wire is used so that potential gradient can be observed easily and can be measured (2) wire having uniform area is taken so that potential gradient value may not change drastically while doing the experiment (3) Emf of driver cell should be greater because as the circuit starts the potential is dropped across the resistor and more emf is needed to drive current in the circuit
Answer:
Potentiometer: It is an instrument that is used for measuring the voltage that is to be found with a known voltage. It is used to determine Electromotive force (emf) and the internal resistance of the cell. Also, it can be used to compare the emf of different cells.
Principle of potentiometer:
"The potential drop across the length of a steady current-carrying wire of uniform cross-section is proportional to the length of the wire".
i) We use long wire so that we get a lower value of the potential gradient.
i.e., a potentiometer with greater sensitivity.
ii) The area of the cross-section has to be uniform to get a uniform wire as per the principle of the potentiometer.
iii) The emf of the driving cell has to be greater than the emf of the primary cells as otherwise there is no balance point would be obtained.
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