What is the unit of electric current?

$(a)$ 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 $XY.$

$(ii)$ 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 ?

What do you mean by heating effect of electric current ? Explain the production of heat in a resistor by flow of electric current through it. Name two devices based on heating effect of current.

A conducting wire offers resistance to the flow of electrons because electrons repel each other in the wire.

$V-I$ graph for a given metallic wire at two temperatures are shown, which of these is for a higher temperature ?

$(a)$ Explain why a conductor offers resistance to the flow of current.

$(b)$ Differentiate between conductor, resistor and resistance.