Practice question

**Energy stored in capacitor** U = ½ C V² = ½ Q V = Q²/(2C) (J), C capacitance (F), V voltage (V), Q charge (C). For 4 μF charged to 250 V, U=0.5×4×10⁻⁶×62500=0.125 J. Energy resides in electric field, energy density u = ½ ε₀ E² (J/m³), E field between plates. Near the center of a large charged conducting plate, the field is approximately uniform ( E = (sigma/ε₀) ), as the plate behaves like an infinite sheet. At the edges, the field lines fringe outward due to the finite size of the plate, leading to a non-uniform field. The charge density sigma may also