A constant-capacitance device has Q = 40 μC at V = 10 V. Sketch its potential–charge graph with V vertical and Q horizontal, shade the area giving its stored energy, and calculate that energy. Explain why the area gives work and identify the graph gradient.

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Straight line through (0,0) and (40 μC,10 V); triangular area 200 μJ; strips VΔQ represent work; gradient 1/C. Label both axes and draw the straight line through the origin and stated point. Shade the triangular area under the line. A small added charge ΔQ requires work VΔQ; summing these strips gives stored energy. W = (1/2) × 40 × 10⁻⁶ × 10 = 2.0 × 10⁻⁴ J. Gradient V/Q = 1/C, not C.

Construct and interpret the energy graph

A constant-capacitance device has Q = 40 μC at V = 10 V. Sketch its potential–charge graph with V vertical and Q horizontal, shade the area giving its stored energy, and calculate that energy. Explain why the area gives work and identify the graph gradient.

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