A cell of internal resistance of 0.2 Ω is connected two cells of resistance 6Ω and 8 Ω joined parallel. There is a current of 0.2 A in the 8 Ω coil. Find the emf of cell.

According to the given information, the electric circuit can be drawn as follows:


Given,
r=0.2Ω
R1=8Ω; I1=0.2A
R2=6Ω
Since 8Ω and 6Ω are in parallel. So the potential difference across in parallel circuit is equal.
i.e. I1R1=I2R2
I2=I1R1R2=0.286=0.27A
Therefore total current (I)=I1+I2=0.2+0.27=0.47A

External Resistance (R)=R1||R2=R1R2R1+R2=686+8=3.4Ω
Now,
ஃ Emf (E)=IR+Ir=I(R+r)=0.47(3.4+0.2)=1.7V

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