Energy stored in a linear capacitor
Charging work produces electric-field energy.
Key knowledge
For a fixed linear capacitance C>0 charged from zero, stored energy is U=Q²/(2C)=CV²/2=QV/2. The factor one-half comes from integrating the rising voltage during charging, not multiplying the final voltage by every charge increment. An ideal vacuum parallel-plate capacitor of area A and gap d has C≈ε₀A/d when edge fields are negligible.
Values and equations
U=∫_0^Q V(q)dq=Q²/(2C)=½CV²; C_parallel_plate≈ε₀A/d
- U
- Stored electric energy relative to uncharged state J
- Q,q
- Terminal charge and integration charge C
- V
- Terminal voltage V
- C,C_parallel_plate
- Capacitance and ideal plate approximation F
- ε₀
- Vacuum permittivity F m⁻¹
- A
- Plate area m²
- d
- Vacuum plate separation m
Conditions and scope
- Fixed geometry and linear reversible dielectric response; Q and V are consistently signed terminal variables with Q=CV.
- Nonlinear/hysteretic dielectric response requires the actual ∫V(Q)dQ and loss model. Stored energy is distinct from energy dissipated in a charging resistance. The plate formula assumes d small relative to lateral dimensions.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read §8.3 energy-density/parallel-plate relation and charging integral8.10. Linear/fixed-response scope qualifies the source’s generic “all capacitors” prose.
2026-10-10 · /root/audit_life_earth_chemistry — independent Chemistry/Life/Earth editor. Independent AI editorial review of this entry's statements, equations, applicability conditions and source coverage. Source checks apply to these claims within their stated limits.
Entry details
Permanent link to this entry ↗- Record identity
- foundation-physics-capacitor-stored-energy
- Revision
- foundations-refresh.1
- Structured reference record
- Foundational reference additions