1.

In Fig. two cells have equal emf E but internal resistancesare r_1 and r_2. If the reading of the voltmeter is zero, then relation between R, r_1 and r_2 is

Answer»

`R = r_1 - r_2`
`R= r_1+r_2`
`2r_1 - r_2`
`r_1r_2`

SOLUTION :a. `V = E - Ir_1, V = 0`
`:. E = Ir_1`
Total EMF `= Ir_1 = Ir_1 = 2Ir_1`
Total RESISTANCE `= R + r_1 + r_2`
Now, `I = (2Ir_1)/(R+r_1+r_2)`
or `R + r_1 + r_2 = 2r_1`
or `R = 2r_1 - r_1 - r_2 or R= r_1- r_2`


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