1. Superposition1 SUPERPOSITION Superposition is a general principle that forms the basis for a very powerful technique used to analyse multisource circuits Restricted to circuits with linear components like resistors Helps when determining the current through or voltage across any component of a multisource circuit Involves the computation of the current or voltage due to each source acting alone Therefore when we begin the computations, we remove all sources except one We make the contributions of the remaining sources (either current source or voltage source) equal to zero We replace ideal voltage sources by short circuits (V = 0) We replace ideal current sources by open circuits (I = 0)

2. Superposition2 PROCEDURE FOR ANALYSING A CIRCUIT USING SUPERPOSITION 1.Select any one source in the circuit and remove all others (by replacing them with short or open circuits) 2.Compute the desired voltage or current in a component when the only source present is the one selected in step 1 3.Repeat steps 1 and 2, after selecting a new source to be the only one present. Continue until the desired voltage or current has been computed due to each and every source acting alone 4.Add all the computed values obtained from analysing the circuit with each source acting alone. The sum is the actual voltage or current when all sources are acting simultaneously (i.e. when all the sources are present) Important to take into account the polarities of the quantities being added. E.g. One source produces a current of 5A from left to right, and another 1A from right to left. The total (net) current is 5+(-1)=4A from left to right Superposition can’t be used to find power dissipated in a resistor, provided computation is carried out after finding current through or voltage across! Don’t add powers. Power is a nonlinear mathematical operation

3. Superposition3 SUPERPOSITION EXAMPLES (1) Using the superposition principle a) Find the current in the 15Ω resistor b) Find the current in the 10Ω resistor.

4. Superposition4 SUPERPOSITION EXAMPLES (2) Using the superposition principle, find the voltage across the 1kΩ and the voltage across the 4kΩ resistor.

5. Superposition5 SUPERPOSITION EXAMPLES (3) To what voltage should the adjustable source E be set in order to produce a current of 0.3A in the 400Ω resistor. If E is set to 30V, to what value should the current source be changed in order that the total current in the 400Ω resistor be 0.3A?