Electrical Circuit Calculations - UFBA（UFBA电路计算）.pdf

Electrical Circuit Calculations Series Circuits Many circuits have more than one conversion device in them (i.e. toaster. heater. lamps etc.) and some have more than one source of electrical energy. If the circuit components are connected end to end to form a single loop it is a series-circuit Remember that current is the rate at which electrons move through the circuit. So as in several hoses connected in series to form one long line, water can only come out at the far end at the same rate that it enters at (neglecting friction). Each component has a volt drop across it (and is the force required to convert the electrical energy to some other form). All of the volt drops in a circuit add up to the e.m.f. (Voltage) of the supply. In the above circuit E = V1 + V2 (This assumes that the connecting wires have very little resistance, which is not an unreasonable assumption to make.) Ammeters Ammeters are instruments that measure current and so have to be in the current path, that is, in series with the device whose current is being measured. The volt drop across each component can be calculated using Ohms law if the circuit current and the value of each components resistance is known. (Remember that the e.m.f of the supply is across the whole circuit and not just across anyone of the components.) Worked Example: • If the circuit shown draws 10 amps from the supply, calculate the volt drop across each resistor and the volume of the supply e.m.f. Note that as it is a series circuit the current is the same in all resistors. V = IR = 10 x 10 = 100V 1 1