In an electric circuit,state the relationship between the direction of conventional current and the direction of flow of electrons.

$(a)$ Name an instrument that measures potential difference between two points in a circuit. Define the unit of potential difference in terms of $SI$ unit of charge and work. Draw the circuit symbols for $(i)$ variable resistor,$(ii)$ a plug key which is closed.
$(b)$ Two electric circuits $(I)$ and $(II)$ are shown below.
$(i)$ Which of the two circuits has more resistance?
$(ii)$ Through which circuit does more current pass?
$(iii)$ In which circuit is the potential difference across each resistor equal?
$(iv)$ If $R_{1} > R_{2} > R_{3}$,in which circuit will more heat be produced in $R_{1}$ as compared to the other two resistors?

Sonika is working with the circuit shown in the figure. There are two open terminals in the circuit: $X$ and $Y$. She has wires made of five different materials: $I, II, III, IV,$ and $V$. She knows that the electric bulb will glow only when wires made of conducting materials are connected across both open terminals. She records her observations in a table. After the experiment,ink spills on the paper,and she loses the information for the third row.

$S.No.$	Material at $X$	Material at $Y$	Electric Bulb ($ON$/$OFF$)
$1$	$I$	$II$	$OFF$
$2$	$I$	$IV$	$ON$
$3$	-	-	$OFF$
$4$	$III$	$V$	$ON$

Based on the remaining information in the table,which materials could be in the third row?

State the factors on which the heat produced in a current-carrying conductor depends. Give one practical application of this effect.

What are the factors on which the resistivity of a material depends?

What is a voltmeter? How is it connected in a circuit?