In an experiment to measure the internal resistance of a cell, by a potentiometer, it is found that the balance point is at a length of $$2$$ m, when the cell is shunted by a $$5$$ resistance and is at a length of $$3$$ m when the cell is shunted by a $$10$$ Ω resistance. The internal resistance of the cell is then

Question

In an experiment to measure the internal resistance of a cell, by a potentiometer, it is found that the balance point is at a length of $$2$$ m, when the cell is shunted by a $$5$$  resistance and is at a length of $$3$$ m when the cell is shunted by a $$10$$ Ω resistance. The internal resistance of the cell is then

Infinity Learn · Accepted Answer

In case of internal resistance measurement by potentiometer,$$V1V2=l1l2=ER1/R1+rER2/R2+r=R1R2+rR2R1+rHere$$ $$l1=2m$$,$$l2=3m$$,$$R1=5$$Ω and $$R2=10$$Ω∴ $$23=5(10+r)10(5+r)or$$ $$20+4r=30+3ror$$ $$r=10$$Ω

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