$A$ student connects a voltmeter,ammeter,and resistance according to the circuit given. If the voltmeter reading is $20\, V$ and the ammeter reading is $4\, A$,then the resistance $R$ will be:

In the given circuit,the reading of the ammeter is ................. $A$ (assume internal resistance of the battery is zero).

The internal resistance of a $2.1\, V$ cell which gives a current of $0.2\, A$ through a resistance of $10\,\Omega$ is ............. $\Omega$.

The reading of the voltmeter is :- .............. $V$

The diagram shows a circuit used in an experiment to determine the $emf$ $(E)$ and internal resistance $(r)$ of the cell $C$. $A$ graph was plotted of the potential difference $V$ between the terminals of the cell against the current $I$,which was varied by adjusting the rheostat. The graph is shown on the right; $x$ and $y$ are the intercepts of the graph with the axes as shown. What is the internal resistance of the cell?

The current flowing through the $1 \Omega$ resistor is $\frac{n}{10} \ A$. The value of $n$ is. . . . . . .