When a resistance of $9 \,\Omega$ is connected across the terminals of a battery,its potential difference decreases from $40 \, V$ to $30 \, V$. The internal resistance of the battery is ............... $\Omega$.

$A$ cell of internal resistance $r$ is connected across an external resistance $n r$. Then the ratio of the terminal voltage to the emf of the cell is

$A$ voltmeter is connected in parallel with a variable resistance $R$ which is in series with an ammeter and a cell as shown in the figure. For one value of $R$,the meters read $0.3 \, A$ and $0.9 \, V$. For another value of $R$,the readings are $0.25 \, A$ and $1.0 \, V$. What is the internal resistance of the cell in $\Omega$?

The potential difference across $A B$ in the network shown is .........

What is the reading of the voltmeter in the following figure (in $V$)?

In the given circuit,if the current flowing through the $5 \Omega$ resistor is $0.5 \text{ A}$,then the value of $E$ is: (in $\text{ V}$)