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Conduction of Electricity

Electric current and the ampere

  • 3 things to know
  • Component 2

Overview

Recall questions on the definition of current as rate of flow of charge, I = Q/t, the coulomb and the ampere, worked conversions between charge, current and time, and counting the electrons that pass in a stated time.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Key term

State the equation linking current, charge and time, defining every symbol and its unit.

Key term

Define electric current.

Key term

Express the ampere in terms of the coulomb and the second.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Define electric current.

    Model answer

    Electric current is the rate of flow of electric charge.

  2. 2

    State the equation linking current, charge and time, defining every symbol and its unit.

    Model answer

    The equation is I = Q/t, where I is the current in amperes (A), Q is the charge transferred in coulombs (C) and t is the time taken in seconds (s).

  3. 3

    Express the ampere in terms of the coulomb and the second.

    Model answer

    One ampere is one coulomb per second, so A = C s⁻¹.

  4. 4

    A charge of 30 C passes a point in a circuit in 2.0 minutes. Calculate the current.

    Model answer

    The current is I = 30 C ÷ 120 s = 0.25 A. Multiplying 0.25 A by 120 s returns the 30 C given.

  5. 5

    A current of 0.50 A flows for 5.0 minutes. Calculate the charge transferred.

    Model answer

    The charge is Q = 0.50 A × 300 s = 150 C. Dividing 150 C by 300 s returns the 0.50 A given.

  6. 6

    How many electrons pass a point when 150 C of charge flows through a metal wire?

    Model answer

    The number is 150 ÷ (1.60 × 10⁻¹⁹) = 9.4 × 10²⁰ electrons. Multiplying 9.375 × 10²⁰ by 1.60 × 10⁻¹⁹ C returns 150 C.

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