A dc potentiometer is designed to measure upto 2 V with a slide wire of 1000 mm. A standard cell of emf 1.5 V obtains balance at 800 mm. A test cell is seen to obtain balance at 750 mm. Which of these statement(s) is/are correct?
A
Emf of test cell is 1.4062 volt
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B
The sensitivity of potentiometer is 0.005 V/mm
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C
Potentiometer works on principle of potential divider
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D
Potentiometer is not accurate.
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Solution
The correct option is C Potentiometer works on principle of potential divider E1= Standard cell of emf 1.5 volt E2=Test cell of unknown emf
(we have to calculate emf) l1 = balancing length of E1, = 800 mm l2 = balancing length of E = 750 mm
⇒ Voltage of any point along the slide wire is proportional to the length of slide wire
E∝l
⇒E2=750800×1.5=1.4062Volt
Sensitivity of potentiometer is given by Vsl
Sensitivity (s) =Vsl=21000=0.002Volt/mm
⇒ Potentiometer works on principle of potential divider