Matter and Electricity
Simple Explanation
Every atom is built from a positively charged nucleus (containing protons and neutrons) surrounded by negatively charged electrons. Ordinary matter becomes charged when electrons are transferred between objects — gaining extra electrons makes an object negatively charged; losing electrons makes it positively charged. Charge always comes in whole-number multiples of the tiny elementary charge, e: Q = ne.
Why Do We Need It?
Understanding that charging is really just electron TRANSFER (never creation or destruction of charge) is the key to the law of conservation of charge — the total charge in an isolated system never changes, only moves around.
Formula
Charge Quantization
Q = ne
Electric charge always comes in whole-number multiples of a single, smallest possible unit — the charge on one electron (or proton). Charge cannot be divided into an arbitrarily small fraction.
- Q
- — total charge, in coulombs (C)
- n
- — the number of electrons (or protons) — a whole number
- e
- — the elementary charge, 1.6 × 10⁻¹⁹ C — the smallest unit of charge
When to use it: Whenever the total charge on an object needs to be found from a number of excess (or missing) electrons, or vice versa.
Worked Example
Find the charge from a number of transferred electrons
An object gains 5 × 10¹² extra electrons. Using e = 1.6 × 10⁻¹⁹ C, find the total charge on the object.
Why Does This Work?
Because every single electron carries exactly the same fixed amount of charge (e), the total charge transferred is simply that fixed amount multiplied by however many electrons moved — which is exactly what Q = ne calculates.
Real-Life Example
Static shocks
Walking across a carpet can transfer millions of electrons onto your body, and touching a metal door handle then gives a small shock.
That shock is literally the excess electrons on your body suddenly flowing (as a tiny electric current) to the door handle, evening out the charge imbalance — a direct, everyday demonstration of electron transfer.
Practice
An object has a charge of −3.2 × 10⁻¹⁸ C. Using e = 1.6 × 10⁻¹⁹ C, find how many excess electrons it has.
MediumCommon mistake
Thinking that charging an object CREATES charge — charging is always just a TRANSFER of existing electrons from one object to another; the total charge in the system is always conserved.
Quick Review
- Atoms: positive nucleus (protons, neutrons) surrounded by negative electrons.
- Charging = electron transfer, not creation.
- Q = ne — charge is always a whole-number multiple of the elementary charge e.