Q35 of 330 Page 41

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?

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


More from this chapter

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34

In the circuit diagram shown below, find:

(i) Total resistance.


(ii) Current shown by the ammeter A


 35

Explain with the help of a labelled circuit diagram, how you will find the resistance of a combination of three resistors of resistances R1, R2 and R3 joined in parallel.

 36

The figure given below shows three resistors


Their combined resistance is:

 37

If two resistors of 35 Ω and 15 Ω are joined together in series and then placed in parallel with a 40 Ω resistor, the effective resistance of the combination is :