Define electric charge, electron, proton, and the coulomb
WHAT is electric charge?
WHY does this matter? Because the entire behaviour of hardware — electrons flowing through copper, transistors switching — is just charges pushing and pulling on each other.
There is no "deeper" explanation of why charge exists; it is a primitive of physics, like mass. We describe what it does, not what it is made of.
WHAT are the electron and proton?
WHY equal and opposite? In a normal atom the number of protons equals the number of electrons, so the atom is neutral (net charge zero). Remove an electron → the atom is now positive (an ion). This exact balance is why bulk matter is usually neutral, and why moving electrons (not protons) is how current flows in a wire.
WHAT is the coulomb?
WHY define a unit at all? "How much charge?" needs a number and a unit, just like "how much water?" needs litres. One electron's charge ( C) is absurdly tiny, so we use a bucket — the coulomb — that holds about 6.24 billion-billion electrons.
HOW to count charge — derivation from first principles
We want a formula linking total charge to number of particles .
Step 1 — State the atom (smallest unit). Charge is quantised: it only comes in whole multiples of . You cannot have half an electron's charge.
Why this step? This is the experimental fact (Millikan's oil-drop experiment) that lets us just count.
Step 2 — Add up identical pieces. If you have particles, each of charge , total charge is simply the sum:
Why this step? Charge is additive — put two charges together and the total is their sum. So counting = multiplication.
Step 3 — Invert to find how many electrons in 1 C.
Why this step? This is exactly the number that defines the coulomb — it's not a coincidence, it's the definition read backwards.
Worked examples
Common mistakes (Steel-manned)
Active recall
Recall Answer before revealing
- What are the two kinds of charge? → positive and negative
- Which particle carries ? → electron
- Value of ? → C
- How many electrons make 1 coulomb? →
- Formula linking charge and count? →
Recall Feynman: explain to a 12-year-old
Imagine tiny invisible marbles. Some are "grumpy" (negative — electrons) and some are "happy" (positive — protons). Grumpy and happy marbles like to stick together, but two grumpies push apart. Electricity is just grumpy marbles (electrons) sliding down a wire. Each marble carries a teeny bit of "charge." Because one marble carries so little, we count them in giant buckets. One bucket-full is called a coulomb, and it holds about six-billion-billion marbles. That's it — electricity is just counting and moving these marbles!
Connections
- Electric Current and the Ampere — current is charge-per-second, .
- Voltage and Potential Difference — the "push" on these charges.
- Conductors and Insulators — whether electrons are free to move.
- Coulomb's Law — the force between two charges.
- Atomic Structure — where protons and electrons live.
What is electric charge?
Which particle carries the smallest free negative charge?
Which particle carries and stays in the nucleus?
What is the elementary charge ?
What is the coulomb?
Formula linking total charge to number of charges?
How many electrons are in 1 coulomb?
Why does an atom lose net charge when it loses an electron?
In a metal wire, which particle actually moves as current?
What does "charge is quantised" mean?
Concept Map
Hinglish (regional understanding)
Intuition Hinglish mein samjho
Dekho, electricity ka sabse basic ingredient hai charge. Charge matter ka ek fundamental property hai — jaise mass hoti hai waise hi charge hoti hai. Ye do type ki hoti hai: positive aur negative. Rule simple hai: same charges ek doosre ko push karte hain (repel), aur opposite charges pull karte hain (attract). Bas itna hi nature ka basic khel hai.
Ab particles: electron chhota sa particle hai jiske paas sabse chhoti negative charge hoti hai, . Proton ke paas exactly utni hi positive charge, , par ye nucleus ke andar bhaari hoke fasa rehta hai. Isiliye wire mein current ke roop mein electrons move karte hain, protons nahi. Jab atom mein protons aur electrons barabar hote hain, atom neutral hota hai. Ek electron nikaal do to atom positive ho jaata hai — usko ion kehte hain.
Coulomb charge ki SI unit hai. Ek electron ki charge itni chhoti hai ( C) ki hum bada bucket use karte hain: 1 coulomb electrons! Formula yaad rakho: , yaani total charge = number of electrons ek electron ki charge. Aur ulta karke, se pata chalta hai kitne electrons hain.
Do galtiyan avoid karo: (1) Coulomb chhota nahi, bahut bada hota hai — ye sirf tezi se flow karta hai isliye circuit mein chhota lagta hai. (2) Current mein protons nahi, electrons chalte hain; "conventional current" sirf ek direction ka convention hai. Ye basics pakke ho gaye to current, voltage, transistors — sab samajhna aasaan ho jayega.