Which equation defines current in terms of charge and time?

• A. V = IR
• B. I = Q / t
• C. P = VI
• D. E = m c^2

Answer: (B)

Current is the rate at which electric charge flows through a point in a circuit. The equation I = Q / t defines current as the amount of charge Q that passes a point divided by the time t over which it passes. This gives the average current over that time interval, and the unit is the ampere (1 A = 1 C/s). For example, if 6 coulombs pass a point in 2 seconds, the current is 3 amperes. The instantaneous current is more precisely dQ/dt, but I = Q/t is the common way to express current for problems involving a defined time interval. The other equations describe voltage, resistance, and power (V = IR, P = VI) or energy-mass equivalence (E = mc^2), not current in terms of charge and time.