series and parallel

• • The electrical power is also defined as the rate of change of work done:
  • The work done is the energy transferred
  • The power is, therefore, the energy transferred per second in an electrical component
• • Rearranging the energy and power equation, the energy can be written as:

  W = Pt = IVt
• • The power of an appliance is:

  The amount of energy transferred (by electrical work) to the device every second
• • A kilowatt-hour is defined as:

  A unit of energy equal to 1 kW of power sustained for 1 hour

  • Or as an equation:

  Energy (kW h) = Power (kW) × Time (h)

  • Since the usual unit of energy is joules (J), this is the 1 W in 1 s
  • Therefore:

  1 kW h = 1000 W × 3600 s = 3.6 × 106 J

  • Since 1 kW = 1000 W and 1 h = 3600 s
  • To convert between Joules and kW h:

  kW h  × (3.6 × 106) = J

  J  ÷ (3.6 × 106) = kW h
• • Kirchhoff’s second law states that:

  The sum of the e.m.f’s in a closed circuit equals the sum of the potential differences
• • In a series circuit, the voltage is split across all components depending on their resistance
  • The sum of the voltages is equal to the total e.m.f of the power supply
  • In a parallel circuit, the voltage is the same across each closed loop
  • The sum of the voltages in each closed circuit loop is equal to the total e.m.f of the power supply:
• • The total voltage of the combined cells can be calculated in the same way as voltage
  • If the cells are connected in series, the total voltage between the ends of the chain of cells is the sum of the potential difference across each cell
  • If the cells are connected in parallel, the total voltage across the arrangement is the same as for one cell