Q. 35 B4.2( 26 Votes )

In the diagram shown below, the cell and the ammeter both have negligible resistance. The resistors are identical

With the switch K open, the ammeter reads 0.6 A. What will the ammeter reading when the switch is closed?

Answer :

When switch is open, the upper two resistances are connected in parallel in the circuit.

Effective resistance is 1/Req=1/R+1/R=2/R

Req = R/2

So the current=I=V/(R/2)=0.6A (given)

V/R = 0.3 A

When the switch closes, the third resistance also comes in the circuit.

The effective resistance of the circuit becomes R/3

Hence, Current I = V/(R/3) = 3 (V/R) = 3 x 0.3 = 0.9 A

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