Last night my daughter came to me for help with a circuit problem that her high school physics teacher had handed out which was identical to figure three of the page at this link except that her voltage and resistors had different values.

http://hallikainen.org/rw/theory/theory6.html

where the assignment was to derive the voltages and currents across each resistor.

Hallikainen said that superposition can be used to solve this by redrawing the circuit as in his figure 4.

Searching for how to do superposition led us to this link, which described how to do superposition analysis very nicely:

http://www.allaboutcircuits.com/vol_1/chpt_10/7.html

My question is that near the end of the page, the allaboutcircuits page says that superposition cannot be used to analyze an unbalanced bridge circuit.

But isn't that what Hallikainen just did? Who's right?

 

Yes he did and he's correct.

 

Indeed, Hallikainen is correct.

Another way to solve the loaded unbalanced bridge is to use the delta to star resistor network transformation for the delta formed by R2, R4 and R5, and then use simple attenuator equations.