Question

Two identical batteries each of emf $E$ = 2 volt and internal resistance $r$ = 1 ohm are available to produce heat in an exlernal resistance by passing a current through it. What is the maximum power that can be developed across an external resistance $R$ using these batteries.

• A. $4W$
• B. $8W$
• C. $6W$
• D. $2W$

Answer 1

The correct option is D $2W$

Given : $E=2$ volts $r=1\Omega$

Equivalent emf in series connection $E_{eq}=E+E=2E=4$ volts

Equivalent resistance in series connection $r_{eq}=r+r=2r=2\Omega$

Maximum power developed $P_{max}=\frac{E_{eq}^2}{4r_{eq}}=\frac{(4{)}^2}{4\left(2\right)}=2$ $W$