From the following diagram: enter image description here

Assume that +V(S), is a applied voltage from a power supply, and current I is flowing now in the circuit, and I introduced a (negatively)changing magnetic flied covering a small volume of that conductor, and an EMF is induced in such a polarity above. The circuit as a whole is like so:


simulate this circuit – Schematic created using CircuitLab

Where (D) is the diagram above the circuit schematic, is total applied voltage on the load equal to the induced EMF added to the applied voltage +V? $$V_t = V_S + V_E$$

Because the induced EMF is now in series with the applied voltage? I guess, my confusion with this is the magnetic field is covering a small area, would the voltage still be additive? Vs. the magnetic field covering a larger area inducing a larger EMF at the same polarity?

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  • \$\begingroup\$ Is this a homework question, or some otherwise synthetic exercise? It doesn't make a lot of sense in any case. BTW you need to specify a reference when talking about voltages. \$\endgroup\$ – Dzarda Apr 4 '15 at 22:50
  • \$\begingroup\$ Why do you say 'current would be I/3'? \$\endgroup\$ – Chu Apr 4 '15 at 23:11
  • \$\begingroup\$ Edited the question. I just want to know what would happen if I placed on of the wires in the parallel circuit part in a changing magnetic field, if we introduce a changing magnetic field to that parallel part of the circuit(3 wires parallel to each other) there is an induced EMF that oppose the power supply, what would happen if only one wire out of those three paralleled ones is in a changing magnetic field that induced a -V or +V depending on the polarity based on the diagram its +V. \$\endgroup\$ – Pupil Apr 5 '15 at 6:45
  • \$\begingroup\$ Sketch the circuit with a battery representing the induced emf. Then you will see the effect this has on the main loop. \$\endgroup\$ – Chu Apr 5 '15 at 10:21
  • \$\begingroup\$ I've done that and posted it above, I find that the first diagram point c would be 25V, and for the second diagram point a would be 15V due to the opposing 5V? \$\endgroup\$ – Pupil Apr 5 '15 at 16:44

Your top diagram doesn't make much sense. However, if you have a closed loop of a power supply and resistor as you show, then the EMF induced by a changing magnetic field enclosed by the loop will add or subract from the power supply voltage, depending on the polarity of the magnetic field change.

You can actually wire this up and see it. Make a circuit of a power, supply, resistor, and the secondary of a transformer, all in series. Assuming the transformer secondary DC resistance is small compared to the resistor, it's effectively not there as long as the primary of the transformer is not driven. When the primary is driven, there will be a corresponding AC voltage induced across the secondary. This secondary is in series with the supply, so the resistor will "see" this voltage plus the supply's voltage at any instance. Note that overall, the transformer will only put out AC, so at times it will add to the supply and at other times subtract from it.

For example, let's say you have a 7 V supply in series with a transformer secondary that puts out 1 V peak AC sine. The resistor will see the voltage varying sinusoidally between 6 V and 8 V.

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  • \$\begingroup\$ Based on the diagram above(looking only at the polarity) the induced EMF adds up to the power supply I guess. Thanks \$\endgroup\$ – Pupil Aug 3 '15 at 0:08

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