4.2 Physics: Energy,Power and Resistance

    Subdecks (1)

    Cards (15)

    • Potential difference is the energy transferred from electrical energy to other forms per unit charge
      V = W/Q
      E.m.f is the energy transferred from other forms e.g. chemical(battery) to electrical per unit charge
    • Speed of electrons =
      eV = 1/2 M * V^2
    • Resistance is the potential difference across a component divided by the current going through it
      R = V/I
    • Ohms law:
      In a ohmic conductor the current is proportional to the potential difference at a constant temperature
    • I/V characteristics:
      Resistor: Resistance is proportional Potential difference, Graph is a straight line through the gradient therefore obeys ohms law, is a ohmic conductor
      R is constant
    • I/V Characteristics:
      Filament lamps: Potential difference does not obey ohms law as Pd is increasing at a faster rate than current
      Resistance increases because as current increases temperature increases therefore more collisions between the electrons and the positive ions
    • I/V Characteristics
      Thermistor:
      Potential difference is not proportional to resistance as current is increasing at a faster rate than pd
      Therefore Resistance decreases because as the temperature increases the number density increases therefore more free conducting electrons
    • I/V characteristics:
      V is not proportional to I therefore does not obey ohms law
      As R decreases as I increases at a faster rate than V
      1 = infinite resistance
      2. At the point of threshold pd starts to conduct
      3. above 3 diode has a small resistance

    • Resistivity =
      L = Lenght
      A = Cross sectional area
    • P = V * I
      Substituting V = I*R in for I and V gives
      P = I^2 * R
      P = V^2/ R
      W = V * I * t
    • Kilowatt hour is the amount of energy used by a 1kw device in one hour
    • Answer:
      Resistance = resistivity * length/ cross sectional area
      Allow values between 220=230
      Question