Superposition theorem question

Hey so just needed to confirm whether I'm doing these questions right.

The circuit is labeled as D attached as P_20160320_145954.jpg
Question b is complete the answer is 5.3 mA

Question c is complete and the answer is 4.69mA

I have no idea how to do question D

All questions are shown in P_20160320_153730

Hmmmm.

You have managed to answer them all incorrectly!

Voltage sources are modelled by:

i) Stating the EMF with a series internal resistance. i.e. the non-ideal voltage source will drop a p.d. across the internal resistance when placed in a series circuit with a load.

Current sources are modelled by:

ii) Stating the current source with a parallel resistance. i.e. the current source will share current with any load resistance also placed in parallel.

Using the above rules makes the answer to the first question c) and not d)


The application of Kirchoff's rule means:
For series circuits, the current must be identical at all points in the current path.
For parallel circuits, the p.d. across all parallel components sharing the same nodes must be identical.


Superposition requires voltage sources to be neutralised by replacing them with a short-circuit and then calculating the current through the load using the remaining current source.

Similarly, current sources are neutralised by replacing them with an open circuit and then calculating the p.d. developed across the load using the remaining voltage source. From that, the current through the load due to the voltage source alone can be calculated.

Current through R2 due to voltage source (current source open circuit):

since the current through the 3k3 load due to the voltage source must be the same as that through the total series resistance.

Current through R2 due to current source (voltage source short circuit):





Hence current through R2 due to current source:



Finally, the actual current through the load is calculated by summing the two answers above taking into account the direction of the currents.

Thank you so much for the help. Just a few things I'm still confused on. So for part b, I 3.3 is the same as It? And I don't understand how you got r parallel. When I nullified the voltage source I got this

you need to learn to quote people in your responses to them, otherwise they will not be aware of your reply.