Three similar cells, each of emf 2 V and internal resistance `rOmega` send the same current through an external resistance of `2Omega`, when connected in series or in parallel. The strength of the current flowing through the external resistance is

Options

A. `1 A`
B. `1.5 A`
C. `2 A`
D. `0.75 A`

Answer

D

Explanation

In series, the effective emf of cells = `3epsilon`, effective internal resistance = 3r where `epsilon` is the emf and r is the internal resistance of each cell. In parallel, the effective emf of cells = `epsilon`, effective internl resistance = `(r )/(3)`
As per question, `I=(3epsilon)/(2+3r)=(epsilon)/(2+(r)/(3))`
or `6+r=2+3rorr=2Omega`
`therefore I=(3xx2)/(2+3xx2)=(6)/(8)=0.75A`