What is the equation for charge in terms of current and time?

What is the equation for charge in terms of current and time?

• A. Charge × Time
• B. Charge × Voltage
• C. Voltage × Time
• D. Current × Time

Answer: (B)

Charge is the amount of electric charge that has flowed, while current is the rate at which charge flows. Since current is the rate of change of charge, I = dQ/dt, we can write dQ = I dt and integrate. If the current is constant, this becomes Q = I t. So the charge is the product of current and time. In units, amperes times seconds equal coulombs. The other expressions don’t describe charge: multiplying charge by time would give a quantity with unusual units, and multiplying charge by voltage yields energy (E = QV). Voltage times time isn’t a standard quantity either. The correct relation is Q = I t.

Charge is the amount of electric charge that has flowed, while current is the rate at which charge flows. Since current is the rate of change of charge, I = dQ/dt, we can write dQ = I dt and integrate. If the current is constant, this becomes Q = I t. So the charge is the product of current and time. In units, amperes times seconds equal coulombs.

The other expressions don’t describe charge: multiplying charge by time would give a quantity with unusual units, and multiplying charge by voltage yields energy (E = QV). Voltage times time isn’t a standard quantity either. The correct relation is Q = I t.