---
title: "Two conducting pendulums of identical dimensions and material are released from rest from the same initial angle to swing through a region of uniform magnetic field directed into the page. Pendulum 1 consists of a solid copper plate, whereas Pendulum 2 has several narrow vertical slots cut into the plate. It is observed that Pendulum 1 rapidly damps and stops after entering the field, while Pendulum 2 continues to swing back and forth freely for a much longer time. Which of the following best explains this observation?"
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url: "https://nerd-notes.com/ubq/121286/"
date_modified: "2026-08-23T04:59:33+00:00"
---

# Two conducting pendulums of identical dimensions and material are released from rest from the same initial angle to swing through a region of uniform magnetic field directed into the page. Pendulum 1 consists of a solid copper plate, whereas Pendulum 2 has several narrow vertical slots cut into the plate. It is observed that Pendulum 1 rapidly damps and stops after entering the field, while Pendulum 2 continues to swing back and forth freely for a much longer time. Which of the following best explains this observation?

Two conducting pendulums of identical dimensions and material are released from rest from the same initial angle to swing through a region of uniform magnetic field directed into the page. Pendulum 1 consists of a solid copper plate, whereas Pendulum 2 has several narrow vertical slots cut into the plate. It is observed that Pendulum 1 rapidly damps and stops after entering the field, while Pendulum 2 continues to swing back and forth freely for a much longer time. Which of the following best explains this observation?

![Two side-by-side pendulum setups are shown. On the left, labeled Pendulum 1, a thin rigid rod extends downward from a pivot to a solid rectangular conducting sheet. On the right, labeled Pendulum 2, an identical rod and sheet are shown, but the sheet contains five evenly spaced, narrow vertical slots cut through it. Below the pivots, a rectangular dashed boundary outlines a region labeled with four small 'x' symbols indicating a magnetic field \vec{B} directed into the page. Curved arrows near the bottom of each sheet point toward the magnetic field region, indicating the direction of swing. No other labels, lines, text, or axes appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787461172-mhRbsw.jpg)

- **A.** The slots interrupt the large circulating eddy-current paths, confining induced currents to smaller loops with higher electrical resistance, which reduces both the total induced current and the resulting magnetic braking force.
- **B.** The slots allow the external magnetic field to pass straight through the plate without exerting magnetic forces on the free electrons, preventing any electromotive force from being induced in the metal.
- **C.** The slots decrease the total surface area of the pendulum plate, reducing the aerodynamic drag force from surrounding air so that mechanical energy is conserved much more effectively.
- **D.** The slots create separate loops where the currents in adjacent strips flow in opposite directions, causing their magnetic fields to cancel out completely and produce zero net retarding force.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/121286/*