Question

"When I apply Kirchoff's loop rule when the switch is closed, the right loop has one battery and two bulbs in series. Thus the potential differences across the battery must equal the sum of potential differeces across the bulbs, so each bulb will get half the potential differences of battery B, and the bulbs will be equally bright."

Identify the flaw(s) in the student's reasoning!

Answer 1

The student's flaw in reasoning is assuming that each bulb will receive half the potential difference of the battery. In reality, the brightness of a bulb depends on its resistance.

Step-by-step explanation:

The flaw in the student's reasoning is related to their understanding of Kirchhoff's loop rule. While it is correct that the potential differences across the battery must equal the sum of potential differences across the bulbs, it does not mean that each bulb will receive half the potential difference of the battery. This assumption is incorrect because the bulbs in the circuit are not identical resistors.

The brightness of a bulb in a circuit depends on the current passing through it. In a series circuit, the current is the same at all points. So, the potential difference across a bulb is directly proportional to its resistance. In the given circuit, both bulbs have the same resistance because they are identical, so they will have the same potential difference across them.

To determine the brightness of the bulbs, you need to consider their individual resistances. If one of the bulbs has a higher resistance than the other, it will receive a smaller potential difference and be less bright. Conversely, the bulb with a lower resistance will receive a larger potential difference and be brighter.