Circuit and electromagnetism basics
Which correctly states Kirchhoff's voltage law (second law)?
- AThe sum of currents flowing into any node equals the sum of currents flowing out
- BThe voltages across series resistors divide in inverse proportion to their resistances
- CAround any closed path in a circuit, the sum of the EMFs equals the sum of the voltage drops
Show answer and explanation
Answer: C. Around any closed path in a circuit, the sum of the EMFs equals the sum of the voltage drops
Kirchhoff's voltage law states that around a closed path (loop), the sum of the source EMFs equals the sum of the voltage drops across the elements—that is, the signed voltages add to zero. Because each point in a circuit has a single potential, going around and returning to the starting point gives a total potential difference of zero. The law about currents at a node is the current law (first law). Writing simultaneous equations from the two laws gives the currents and voltages throughout a circuit.
- A. This is the current law (first law), which concerns nodes.
- B. Voltages across series resistors divide in proportion to their resistances.
- C. Correct. The voltages around a closed path add to zero.
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