Electric charge is a fundamental property of matter. This guide covers properties, units, measurement, and applications.
What is Electric Charge?
Determines electromagnetic interaction. Two types: positive and negative. Like repels, unlike attracts.
Key Properties:
- Quantized (multiples of e)
- Conserved (transferred only)
- Invariant (frame‑independent)
Units of Electric Charge
Coulomb (C)
SI unit; charge moved by 1 A in 1 s.
1 C = 6.242 × 10¹⁸ e
Elementary charge (e)
Charge of proton (magnitude of electron).
e = 1.602176634 × 10⁻¹⁹ C
Charge Conversion Table
| Unit | C | e | Ah | statC |
|---|---|---|---|---|
| 1 C | 1 | 6.242 × 10¹⁸ | 0.0002778 | 2.998 × 10⁹ |
| 1 e | 1.602 × 10⁻¹⁹ | 1 | 4.450 × 10⁻²³ | 4.803 × 10⁻¹⁰ |
| 1 Ah | 3,600 | 2.247 × 10²² | 1 | 1.079 × 10¹³ |
| 1 statC | 3.336 × 10⁻¹⁰ | 2.082 × 10⁹ | 9.266 × 10⁻¹⁴ | 1 |
Types of Electric Charge
Positive Charge
- Protons
- Positive sign
- Equal magnitude to electron
Negative Charge
- Electrons
- Negative sign
- Equal magnitude to proton
Did You Know?
Greeks observed static electricity using amber (~600 BCE).
Charge in Atoms and Materials
Neutral: protons = electrons. Gaining/losing electrons forms ions.
Conductors
Charge flows easily (metals, graphite).
Insulators
Resist flow (rubber, glass, plastic).
Semiconductors
Intermediate (silicon, germanium).
Applications of Electric Charge
Electronics
- ICs
- Transistors, diodes
- Capacitors, batteries
Energy
- Batteries, fuel cells
- Generation
- Storage
Medical
- ECG
- Defibrillators
- Imaging
Industry
- Electroplating
- Electrostatic paint
- Air purification
Practical Tip:
Discharge static before handling ICs; use a grounded wrist strap.
Measuring Electric Charge
Electrometers
Very high input impedance.
Coulombmeters
Direct charge in coulombs.
Integrating ammeters
Q = I × t.
Charge in Everyday Life
Static Electricity
- Doorknob shocks
- Clothes cling
- Balloon to wall
Batteries
Redox moves electrons from − to + terminal.
Lightning
Huge atmospheric spark (hundreds of MV, up to ~200 kA).