Electrical Circuit
Electricity and Magnetism

Energy in series and parallel connections

Physics Narrative for 14-16 Supporting Physics Teaching

How energy is shifted in circuits with different connections

Two lamps connected in parallel each glow as brightly as one connected by itself. By now you might expect this, because lamps are often used as informal ammeters in classrooms, and the potential difference is the same across both lamps. So twice as much energy is being shifted in the circuit with parallel connections compared with the simple circuit with only one lamp. The consequence is that the chemical store of energy associated with the battery is depleted twice as much after the circuits have been running for identical lengths of time.

Two lamps connected in series deplete the battery much less, because the current in the circuit is smaller than in the circuit with only a single lamp and battery, and the potential difference is the same for both circuits. Less energy is shifted by the two lamps compared with the single lamp.

Power in pathway and time determine energy shifted to store

The same patterns of dissipation of energy apply to resistors, only these don't glow (at least visibly, but they may radiate at frequencies below those that we can see, perhaps in the infrared). Resistors shift some energy to a thermal store using the heating by radiation pathway, and typically much more energy using the heating by particles pathway.

To calculate exactly how much energy is shifted during 1 second in each lamp in all of the situations, you need to determine how much electrical working is happening: the power in the electrical pathway. That is the focus of episode 02.

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