question_answer

Two identical batteries, each of emf 2 V and internal resistance \[1\,\Omega \]pass a current through external resistance \[R=0.5\,\Omega .\]The maximum power that can be developed across R using these batteries is:

A)  3.2W           

B)  8.2W

C)  4 W             

D)  2 W

Correct Answer: D

Solution :

 Key Idea: In pardllel combination positive poles of all cells are connected to one point and negative poles to another point. The resistances of \[1\,\Omega \] are connected in parallel hence, equivalent resistance of combination is \[{{r}_{eq}}=\frac{1\times 1}{1+1}=0.5\] From Ohms law, \[E=i(R+r)\] \[\therefore \] \[i=\frac{2}{0.5+0.5}=2A\] Power is given by \[P={{i}^{2}}R={{(2)}^{2}}\times 0.5=2W\]