What is Electric Charge?
Electric charge is a fundamental property of matter that causes particles to experience a force in an electric field. It comes in two kinds, positive and negative, and is always quantized in multiples of the elementary charge carried by a single electron or proton.
Electric charge (symbol q or Q) is the physical property that gives rise to electric and magnetic forces; it is measured in coulombs (C) and can be related to current and time by Q = I × t.
- •Carried by protons
- •Deficit of electrons
- •Attracts negative charges
- •Repels other positive charges
- •Carried by electrons
- •Excess of electrons
- •Attracts positive charges
- •Repels other negative charges
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Step-by-step worked examples
A wire carries a steady current of 3 A for 5 seconds. How much charge flows through it?
Q = I × t Q = 3 × 5 = 15 C
A capacitor accumulates 40 C of charge from a 0.5 A charging current. How long did it charge?
Q = I × t → t = Q / I t = 40 / 0.5 = 80 s
How much charge does a 2 A current deliver in 1 minute?
t = 60 s Q = I × t = 2 × 60 = 120 C
Flashcards
Quick quiz
Q1.What is the SI unit of electric charge?
Q2.A 4 A current flows for 10 s. What charge passes?
Q3.Which statement about charge is true?
Q4.Two positive charges are brought close together. What happens?
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Common mistakes
Thinking charge can take any arbitrary value. — Correct: Charge is quantized — always a whole-number multiple of e.
Confusing current and charge. — Correct: Current is the rate of charge flow (I = Q/t); charge is the total amount.
Believing charge can be destroyed. — Correct: Charge is conserved — it can move but the total stays constant in an isolated system.
Assuming opposite charges repel. — Correct: Opposite charges attract; like charges repel.
FAQ
What is electric charge?
Electric charge is a fundamental property of matter that produces electric and magnetic forces, measured in coulombs (C).
What is the electric charge formula?
Charge relates to current and time by Q = I × t, where I is current in amperes and t is time in seconds.
What are examples of electric charge?
Protons (+e), electrons (−e), a charged balloon after rubbing on hair, and the charge stored in a capacitor are all examples.
How do you calculate electric charge?
Multiply the current by the time it flows: Q = I × t. For example, 3 A for 5 s gives 15 C.