(a) Name an instrument that measures electric current in a circuit. Define the unit of electric current.
(b) What do the following symbols, (Fig. 3.58) mean in a circuit diagram ?

(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) Graph shown in (Fig. 3.59) was plotted `V and I` values.
What would be the values of `V//I` ratios when the potential differences are `0.8 V, 1.2 V and 1.6 V` respectively ? What conclusion do you draw from these values ?
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