---
title: "A circuit consists of an ideal battery of electromotive force \\(\\mathcal{E}\\), four identical lightbulbs labeled 1, 2, 3, and 4 each with constant resistance \\(R\\), and an open switch \\(S\\), as shown in the diagram. Switch \\(S\\) is connected in parallel across Bulb 3.  | Option | Brightness of Bulb 2 | Brightness of Bulb 4 | Potential Difference Across Bulb 1 | | :— | :— | :— | :— | | (A) | Decreases | Decreases | Increases | | (B) | Increases | Remains unchanged | Increases | | (C) | Decreases | Increases | Decreases | | (D) | Increases | Decreases | Increases |  Which row in the table correctly describes the resulting changes in the circuit after switch \\(S\\) is closed?"
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url: "https://nerd-notes.com/ubq/120463/"
date_modified: "2026-08-23T04:34:55+00:00"
---

# A circuit consists of an ideal battery of electromotive force \(\mathcal{E}\), four identical lightbulbs labeled 1, 2, 3, and 4 each with constant resistance \(R\), and an open switch \(S\), as shown in the diagram. Switch \(S\) is connected in parallel across Bulb 3.

| Option | Brightness of Bulb 2 | Brightness of Bulb 4 | Potential Difference Across Bulb 1 |
| :— | :— | :— | :— |
| (A) | Decreases | Decreases | Increases |
| (B) | Increases | Remains unchanged | Increases |
| (C) | Decreases | Increases | Decreases |
| (D) | Increases | Decreases | Increases |

Which row in the table correctly describes the resulting changes in the circuit after switch \(S\) is closed?

A circuit consists of an ideal battery of electromotive force \(\mathcal{E}\), four identical lightbulbs labeled 1, 2, 3, and 4 each with constant resistance \(R\), and an open switch \(S\), as shown in the diagram. Switch \(S\) is connected in parallel across Bulb 3.

| Option | Brightness of Bulb 2 | Brightness of Bulb 4 | Potential Difference Across Bulb 1 |
| :--- | :--- | :--- | :--- |
| (A) | Decreases | Decreases | Increases |
| (B) | Increases | Remains unchanged | Increases |
| (C) | Decreases | Increases | Decreases |
| (D) | Increases | Decreases | Increases |

Which row in the table correctly describes the resulting changes in the circuit after switch \(S\) is closed?

![A rectangular schematic diagram of a DC circuit. On the left vertical wire is a DC voltage source labeled \(\mathcal{E}\), with the longer positive terminal on top. The wire extends from the positive terminal to the right along the top rail, passing through Bulb 1. After Bulb 1, the circuit splits at a junction into an upper branch and a lower branch. The upper branch contains Bulb 2 connected in series with Bulb 3, where an open switch \(S\) is connected across the terminals of Bulb 3 on a parallel bypass segment. The lower branch contains Bulb 4. The upper and lower branches rejoin at a right junction, which connects to the bottom horizontal rail returning to the negative terminal of the voltage source. Each bulb is represented as a circle with an internal filament loop. No other labels, lines, components, or text appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787459695-oNu9BV.jpg)

- **A.** Row A
- **B.** Row B
- **C.** Row C
- **D.** Row D

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120463/*