series and parallel

Cards (7)

    • 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:
    = 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