Electricity AS

Cards (34)

  • There are three key quantities: V, I, and R
  • Current (I)

    The rate of flow of charge particles
  • Conventional current
    Flows from positive to negative, but the actual charge carriers (electrons) move from negative to positive
  • Potential difference (V)
    The energy transferred per unit charge
  • Resistance (R)

    The ratio of potential difference across a component to the current in that component
  • Investigating component characteristics
    1. Set up circuit with ammeter and voltmeter
    2. Vary current/potential difference
    3. Measure current and potential difference
  • IV characteristics
    • Relationship between current (I) and potential difference (V)
    • For ohmic conductors, a straight line through the origin
    • For non-ohmic conductors, a non-linear relationship
  • Ohm's law states that current is proportional to potential difference, provided physical conditions are constant
  • Resistance
    Not always equal to 1 over the gradient of the IV characteristic
  • IV characteristics
    • Resistor: straight line through origin
    • Filament lamp: non-linear
    • Diode: allows current flow in one direction only
  • Resistivity (ρ)

    A material property that determines the resistance of a conductor based on its length and cross-sectional area
  • As temperature increases
    Resistance of most materials increases
  • Semiconductors
    As temperature increases, resistance decreases due to more charge carriers being liberated
  • Superconductors
    Below a critical temperature, resistance drops to zero
  • Kirchhoff's first law: the sum of currents into a junction equals the sum of currents out of the junction
  • EMF (ε)
    The energy per unit charge transferred to the circuit by a source (e.g. battery)
  • Around any closed loop in a circuit, the sum of the EMFs equals the sum of the potential differences
  • EMF
    Energy transferred to the circuit by a battery
  • Potential difference
    Energy transferred within a component
  • Around any closed loop in the circuit

    The sum of the EMFs is equal to the sum of the potential differences
  • Series circuit
    • Current is the same everywhere in the circuit
  • Parallel circuit

    • Current is split at a junction
  • In a parallel circuit

    The potential difference is the same across each component
  • Total resistance in series circuit

    Sum of individual resistors
  • Total resistance in parallel circuit
    1 over (1/r1 + 1/r2 + ...)
  • Power
    Rate of energy transfer = IV = I^2R = V^2/R
  • Total energy transferred
    Power x time = IVt
  • Potential divider circuit
    • Splits potential difference between two resistors
  • Potential divider components
    • Thermistor
    • Light dependent resistor
    • Variable resistor
  • Internal resistance
    Resistance within a cell or power supply
  • EMF
    Equal to terminal potential difference + current x internal resistance
  • As current increases
    Terminal potential difference decreases
  • Cells in series
    Internal resistances add up
  • Cells in parallel

    Combined internal resistance decreases