Current and Circuit Symbols

• Current


  The flow of electric charge
• Current flow


  1. Requires a complete (closed) circuit

  2. Requires a potential difference source
• Unit of current


  Ampere, A
• In a single, closed loop circuit the current has the same value everywhere
• Potential difference (voltage)


  The driving force that pushes the charge round
• Unit of potential difference

  Volt, V
• Resistance


  Anything in the circuit which slows the flow down
• Unit of resistance


  Ohm, Ω
• Current flowing through a component

  Depends on the potential difference across it and the resistance of the component
• Greater resistance across a component


  Smaller the current that flows through it (for a given potential difference)
• Total charge through a circuit

  1. Depends on current and time

  2. Charge (C) = Current (A) x Time (s)

  3. Q = It
• Unit of charge


  Coulomb, C
• More charge passes around the circuit when a bigger current flows