---
title: "An uncharged parallel-plate capacitor of capacitance \\(C_0\\) is connected in series with a resistor of resistance \\(R\\) and an ideal battery of emf \\(\\mathcal{E}\\). At time \\(t = 0\\), the switch is closed. At a later time \\(t_1\\) while the capacitor is actively charging, a slab of dielectric with dielectric constant \\(\\kappa > 1\\) is suddenly inserted, completely filling the space between the plates. Which of the following best describes the current through the resistor immediately after the dielectric is inserted, compared to immediately before, along with the correct justification?"
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url: "https://nerd-notes.com/ubq/118401/"
date_modified: "2026-08-04T08:09:55+00:00"
---

# An uncharged parallel-plate capacitor of capacitance \(C_0\) is connected in series with a resistor of resistance \(R\) and an ideal battery of emf \(\mathcal{E}\). At time \(t = 0\), the switch is closed. At a later time \(t_1\) while the capacitor is actively charging, a slab of dielectric with dielectric constant \(\kappa > 1\) is suddenly inserted, completely filling the space between the plates. Which of the following best describes the current through the resistor immediately after the dielectric is inserted, compared to immediately before, along with the correct justification?

An uncharged parallel-plate capacitor of capacitance \(C_0\) is connected in series with a resistor of resistance \(R\) and an ideal battery of emf \(\mathcal{E}\). At time \(t = 0\), the switch is closed. At a later time \(t_1\) while the capacitor is actively charging, a slab of dielectric with dielectric constant \(\kappa > 1\) is suddenly inserted, completely filling the space between the plates. Which of the following best describes the current through the resistor immediately after the dielectric is inserted, compared to immediately before, along with the correct justification?

![A schematic of a single-loop RC circuit drawn with clean black lines. On the left vertical branch, an ideal battery symbol is labeled with the text \(\mathcal{E}\). On the top horizontal branch, a resistor is drawn as a zig-zag line labeled \(R\). On the right vertical branch, a parallel-plate capacitor is shown as two parallel horizontal plate segments labeled \(C_0\). A shaded rectangular slab labeled with dielectric constant \(\kappa\) is shown positioned partially between the plates, with an arrow pointing into the gap indicating insertion. A closed switch symbol is located on the bottom horizontal branch. No other labels, text, or circuit components appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1785830995-S49uYH.jpg)

- **A.** The current decreases because the increase in capacitance increases the time constant \(\tau = RC\), which slows the rate at which charge flows through the circuit.
- **B.** The current decreases because inserting the dielectric increases the opposing electric field inside the capacitor, reducing the voltage drop across the resistor.
- **C.** The current increases because the insertion of the dielectric causes an instantaneous jump in the charge stored on the capacitor while maintaining a constant capacitor voltage.
- **D.** The current increases because the increased capacitance decreases the potential difference across the capacitor, thereby increasing the potential drop across the resistor.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/118401/*