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In Fig. A2.6, two cells have equal emf E...

In Fig. A2.6, two cells have equal emf E but internal resistances are `r_1 and r_2`. If the reading of the voltmeter is zero, then relation between R, `r_1 and r_2` is

A

`R = r_1 - r_2`

B

`R= r_1+r_2`

C

`2r_1 - r_2`

D

`r_1r_2`

Text Solution

Verified by Experts

The correct Answer is:
A
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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