What are the factors on which heat dissipated by a conductor depends?

$A$ thick wire and a thin wire of the same material are successively connected to the same circuit to find their respective resistance. Which one will have lower resistance? Give reason.

$(a)$ Name an instrument that measures electric current in a circuit. Define the unit of electric current.
$(b)$ What do the following symbols mean in circuit diagrams?
$(c)$ An electric circuit consisting of a $0.5 \ m$ long nichrome wire $XY$,an ammeter,a voltmeter,four cells of $1.5 \ V$ each and a plug key was set up.
$(i)$ Draw a diagram of this electric circuit to study the relation between the potential difference maintained between the points $X$ and $Y$ and the electric current flowing through $XY$.
$(ii)$ The following graph was plotted between $V$ and $I$ values. What would be the values of $V/I$ ratios when the potential difference is $0.8 \ V$,$1.2 \ V$ and $1.6 \ V$ respectively? What conclusion do you draw from these values?

Explain the term resistance. Give its $SI$ unit of measurement.

Which particles are responsible for the flow of current in conductors?

$1 \, \mu A = \ldots \ldots \ldots \, A$