The balancing lengths of potentiometer wire are l1 and l2 when two cells of emf E1 and E2 are connected in the secondary circuit in series. first to support each other and next to oppose each other. Then the ratio of E1E2 is equal to [if E1>E2]
A
l1−l2l1+l2
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B
l1+l2l1−l2
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C
l1l2
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D
l2l1
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Solution
The correct option is Bl1+l2l1−l2 For support each other :
(E1+E2)∝l1⇒E1+E2=xl1......(1)
For Oppose each other :
(E1−E2)∝l2⇒E1−E2=xl2.....(2)
On dividing (1) and (2),
E1+E2E1−E2=l1l2
By componendo and dividendo method.
(E1+E2)+(E1−E2)(E1+E2)−(E1−E2)=l1+l2l1−l2
2E12E2=l1+l2l1−l2
E1E2=l1+l2l1−l2
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Hence, (B) is the correct answer.