Estimate field energy from charge spacing or capacitor storage with confidence today. Compare dielectric media, convert units, and export results for reports fast easily.
Point charges: U = (k · q1 · q2) / r, where k = k0 / εr and k0 ≈ 8.9875517923×10⁹ N·m²/C².
Capacitor energy: U = ½·C·V² or U = ½·Q·V or U = Q²/(2·C).
Units: C in coulombs, r in meters, C (capacitance) in farads, V in volts, energy in joules.
| Scenario | Inputs | Expected behavior |
|---|---|---|
| Attractive charges | q1 = +2 µC, q2 = −3 µC, r = 5 cm, εr ≈ 1 | Negative energy; magnitude grows as r decreases |
| Repulsive charges | q1 = +2 µC, q2 = +3 µC, r = 5 cm, εr ≈ 1 | Positive energy; reduced if εr is larger |
| Capacitor (CV²) | C = 10 µF, V = 12 V | Positive energy increasing with C and V² |
| Capacitor (Q²/2C) | C = 10 µF, Q = 120 µC | Positive energy increasing with Q² |
These examples are for sanity checks and training.
Electrostatic energy quantifies work needed to assemble charges or charge a capacitor. In electronics, it predicts stored energy in filters and flash circuits. In physics labs, it estimates interaction strength at small separations. In safety reviews, it helps assess discharge risks when capacitance and voltage are known and controlled carefully.
For two point charges, the calculator applies U = k·q1·q2/r, where k depends on the medium. This model is most reliable when charges are small compared with separation distance and can be treated as points. It is commonly used for charged spheres, ions, and simplified Coulomb interactions in many textbooks.
Materials reduce field strength through relative permittivity εr. The tool uses k = k0/εr with k0 ≈ 8.9875517923×10^9 N·m²/C². For air, εr is close to 1; for water, εr is about 78, strongly reducing interaction energy magnitude at the same geometry at room temperature in many cases.
Energy sign carries meaning. If q1 and q2 have opposite signs, U becomes negative, indicating an attractive system with lower energy than infinite separation. Same-sign charges yield positive U, representing repulsion and required work to bring charges closer. Magnitude grows as r decreases and as charges increase very quickly.
Capacitors store energy in the electric field between conductors. The calculator offers U = ½·C·V² for voltage-driven cases, U = ½·Q·V when charge and voltage are known, and U = Q²/(2·C) for charge-driven analyses. These forms are equivalent when C, V, and Q are consistent for ideal, linear dielectric capacitors.
Inputs can be entered in practical units, then converted internally to base units for computation. Charges convert to coulombs, distances to meters, and capacitance to farads. Results are shown in joules and electronvolts, plus scaled units such as mJ or µJ. This improves readability across small and large energies directly.
Use quick checks to catch unrealistic inputs. For point charges, r must be positive and not near zero; otherwise the model diverges. For capacitors, energy rises with V², so doubling voltage quadruples energy. Typical small capacitors at 12 V store millijoules, while large banks can reach kilojoules and reduce mistakes.
Clear reporting improves repeatability. After calculating, download CSV for spreadsheets or PDF for sharing in notes. Record the chosen εr and unit selections to reproduce results. When comparing scenarios, keep geometry constant and vary one parameter at a time. Good documentation turns calculations into reliable decisions for audits and reviews.
It is the energy associated with electric fields from charges or a charged capacitor. The tool computes interaction energy for point charges, or stored field energy for capacitors, using standard textbook formulas and consistent unit conversions.
Negative energy occurs when charges have opposite signs, meaning the system is bound and would release energy as charges come together. Positive energy indicates repulsion and the required work to decrease separation.
Choose the medium that best matches your setup: air for open lab conditions, vacuum for idealized problems, or a material like water or oil if fields exist inside that material. Use custom εr when you have a measured value.
Use capacitor mode when you know capacitance with voltage or charge, such as in power supplies, timing networks, and energy storage. Use point charges when modeling interactions between localized charges separated by distance.
Yes. You can use units down to nanometers and picocoulombs. However, extremely small separations may violate the point-charge assumption or require quantum or material effects not included in this simple model.
Electronvolts are convenient for microscopic scales where joules are tiny. Converting to eV helps compare energies to atomic and particle processes while keeping the primary result in joules for engineering contexts.
Presets are typical reference values and can vary with temperature, frequency, purity, and composition. For higher accuracy, measure or reference the exact material data for your conditions and enter a custom εr.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.