2.1.2 Charge & Current

• Charge (Q)

  Electric charge is a fundamental property of matter that causes it to experience a force in an electric field
• Types of Charge

  • Positive Charge
  • Negative Charge
• Positive Charge


  Carried by protons
• Negative Charge


  Carried by electrons
• The total charge in an isolated system remains constant
• Conservation of Charge

  This principle is known as the conservation of charge
• Quantization of Charge

  Charge is quantized, meaning it exists in discrete amounts
• The smallest unit of charge is the charge of an electron, which is approximately 1.6×10−19 coulombs
• Calculating Charge

  Q=I×t
• Electric current (I)


  The rate at which charge flows through a conductor or circuit
• Conventional Current

  Flow of positive charge from the positive to the negative terminal of a power source
• Electron Flow


  Actual movement of electrons from the negative to the positive terminal
• Current Formula

  I=Q/t
• The current in a circuit is the flow of charge per unit time
• If a circuit has a constant current


  The amount of charge passing through any cross-section of the circuit per unit time is constant
• Instruments for Measuring Charge and Current

  • Ammeter
  • Coulomb Meter
  • Voltmeter
• Ammeter


  Measures current and is connected in series with the circuit
• Coulomb Meter


  Measures total charge accumulated over time
• Voltmeter


  Measures voltage across components but is connected in parallel
• Ohm’s Law


  Relates current (I), voltage (V), and resistance (R) in a circuit
• Ohm's Law Formula


  V=I×R
• Finding Current

  I=V/R
• Series Circuits


  The same current flows through all components
• Total Resistance in Series

  Rtotal=R1+R2+⋯
• Parallel Circuits

  The total current is the sum of the currents through each parallel branch
• Total Resistance in Parallel


  1/Rtotal=1/R1+1/R2+⋯
• Current flows through components like resistors, LEDs, and transistors to perform functions
• Batteries provide a source of charge that flows through circuits when a device is turned on