Electric Charge: A Fundamental Property of Matter | Change Unit
Electric charge underpins all of electronics, chemistry, and electromagnetism. From the charge stored in a lithium-ion battery (measured in milliampere-hours) to the charge on a capacitor in a camera flash, understanding charge units and conversions is critical for engineers, students, and anyone working with electronics.
What Is Electric Charge?
Electric charge is an intrinsic property of subatomic particles. Protons carry a positive charge of +e; electrons carry −e. Objects with the same sign repel; opposite signs attract. This interaction is described by Coulomb's Law.
The SI Unit: Coulomb (C)
The coulomb is defined as the charge transported by a current of one ampere in one second: 1 C = 1 A·s. One coulomb equals approximately 6.242 × 10¹⁸ elementary charges.
Common Charge Units and Conversions
| Unit | Symbol | Equivalent | Use Case |
|---|---|---|---|
| Coulomb | C | 1 C = 1 A·s | Capacitors, physics |
| Millicoulomb | mC | 0.001 C | Small capacitors |
| Microcoulomb | µC | 10⁻⁶ C | Electrostatics |
| Milliampere-hour | mAh | 3.6 C | Battery capacity |
| Ampere-hour | Ah | 3,600 C | EV batteries, power banks |
| Faraday | F | ≈ 96,485 C | Electrochemistry (1 mol e⁻) |
Battery Capacity: mAh vs. Coulombs
Battery capacity is almost always listed in milliampere-hours (mAh). To convert: Charge (C) = Capacity (mAh) × 3.6. A 5,000 mAh power bank stores 18,000 C of charge.
Charge in Capacitors
A capacitor stores charge according to Q = C × V, where C is capacitance in farads and V is voltage. A 100 µF capacitor charged to 5 V holds 500 µC of charge.
FAQs
Q: Is charge the same as current?
A: No. Current is the rate of charge flow (charge per second). Charge is the quantity itself.
Q: How do I convert Ah to coulombs?
A: Multiply by 3,600. Example: 2 Ah = 7,200 C.