Q.

Two ideal batteries of emf V1 and V2 and three resistances R1, R2 and R3 are connected as shown in the figure. The current in resistance R2 would be zero if      [2014]

1 V1=V2 and R1=R2=R3  
2 V1=V2 and R1=2R2=R3  
3 V1=2V2 and 2R1=2R2=R3  
4 2V1=V2 and 2R1=R2=R3  

Ans.

(1, 2, 4)

No current is flowing through resistance R2.

Applying KVL in loop

V1-iR1+V2-iR3=0

  i=V1+V2R1+R3                 (i)

Applying KVL in loop BCDEB

V1-iR1=0

  i=V1R1               (ii)

From eq. (i) & (ii)

V1R1=V1+V2R1+R3

  V1R1+V1R3=V1R1+V2R1

  V1R3=V2R1

If V1=V2, then R1=R3=R2

If V1=V2, then R1=R3=2R2

If V1=2V2, then 2R3=R1

If 2V1=V2, then R3=2R1=R2