Step 1: Understand the concept
In an AC circuit with a pure capacitor, the current leads the emf (voltage) by a phase angle of \(90^\circ\), or \(\frac{\pi}{2}\). Phasors rotate anticlockwise, so the leading phasor is \(90^\circ\) ahead in the anticlockwise direction.
Step 2: Read the figure
Diagram (A) shows both phasors along the same direction, meaning they are in phase (a pure resistor). Diagram (B) shows \(e_c\) along the horizontal direction and \(I_c\) pointing up, \(90^\circ\) ahead anticlockwise of \(e_c\). Diagram (C) shows \(I_c\) pointing down, \(90^\circ\) behind \(e_c\). Diagram (D) shows the two in opposite directions, a phase difference of \(180^\circ\).
Step 3: Match
Only diagram (B) shows the current ahead of the emf by \(90^\circ\), so it represents the capacitor.
Step 4: Result
The figure labels its four drawings (A) to (D), and the question options point to them in a different order. The drawing labelled (B) is the third option of the question, which is option (C). The drawing labelled (C) shows the current lagging, as in an inductor.
Final Answer:
Diagram (B) shows the current leading the emf by 90 degrees. This is option (C).
\[ \boxed{\text{(C) }\text{Diagram (B)}} \]
