Equivalents and the load question

Two of the four tools answer a question about a circuit instead of solving it. Both take a pair of nodes.

Equivalent resistance

Find equivalent → Resistance / impedance, with the two nodes.

Three resistors and no source: a 100 Ω in series with a 200 Ω and a 300 Ω in parallel, and the question is the resistance of the whole seen from its two ends. We name them r1 to r3, call the free end node 1 and the junction node 2, and put the far end on ground:

r1,1,2,100
r2,2,0,200
r3,2,0,300

Open Find equivalent, choose Resistance / impedance, and give the two nodes 1 and 0:

100 Ω in series with 200 ‖ 300. No source is needed and none is present: this is a question about the network, not about a circuit that runs.

If the circuit does contain independent sources, they are suppressed first — voltage sources shorted, current sources opened — which is the textbook procedure. Dependent sources are not suppressed, because they are part of the network's behaviour.

In AC the same tool returns an impedance, and the menu says so.

Thévenin and Norton

Find equivalent → Thévenin / Norton, with the two nodes. One run returns both forms, because they are the same two numbers.

A 20 V source and a divider of 50 Ω and 150 Ω, and the question is what the circuit looks like from the divider's midpoint: a single source behind a single resistance. We describe the three elements, naming them e, r1 and r2, and call the midpoint node 2:

e,1,0,20
r1,1,2,50
r2,2,0,150

Open Find equivalent, choose Thévenin / Norton, and give the two terminals 2 and 0:

The Norton current is reported in the direction it actually flows, from the first node to the second. Carry the sign through rather than assuming a positive value.

A fourth answer comes with those three, unasked:

pmax is the maximum power transfer result — the power delivered when the load equals R_eq, which for this circuit is 15²/(4×37.5).

The load question

Under the two node boxes is a tick: Are you running a problem with a load connected to this equivalent circuit? It adds three more answers, each an expression in a symbol load:

Give load a value in Define and all three become numbers.