$A$ cell of $emf\;4\,V$ and internal resistance $0.5\,\Omega$ is connected to a $7.5\,\Omega$ external resistance. The terminal potential difference of the cell is $.....\,V$.

For an open circuit condition,what is the value of the terminal voltage of a cell?

It is easier to start a car engine on a hot day than on a cold day. This is because the internal resistance of the car battery

The reading of a high resistance voltmeter when a cell is connected across it is $2.2\, V$. When the terminals of the cell are also connected to a resistance of $5\,\Omega$,the voltmeter reading drops to $1.8\, V$. Find the internal resistance of the cell in $\Omega$.

$A$ cell of emf $10 \text{ V}$ and internal resistance $3 \Omega$ is connected in parallel with another cell of emf $7 \text{ V}$ and internal resistance $\frac{3}{5} \Omega$,such that their positive terminals are joined together and their negative terminals are joined together. Their combined positive terminal is joined with the negative terminal,and their combined negative terminal is joined with the positive terminal of a third cell of emf $20 \text{ V}$ with internal resistance $2 \Omega$. The combination can be replaced by a battery of emf $E$ and internal resistance $r$. The values of $E$ and $r$ are respectively:

Two identical batteries, each of $e.m.f.$ $2\,V$ and internal resistance $1.0\,\Omega$, are available to produce heat in an external resistance $R = 0.5\,\Omega$ by passing a current through it. The maximum Joulean power that can be developed across $R$ using these batteries is ............. $W$.