---
title: "A velocity selector consists of two horizontal parallel conducting plates producing a uniform downward electric field of magnitude \\(E\\), and a uniform magnetic field of magnitude \\(B\\) directed into the page throughout the region between the plates. Positively charged ions of charge \\(+q\\) enter the region horizontally to the right with speed \\(v\\). If the ions enter with a speed \\(v > \\dfrac{E}{B}\\), towards which plate do the ions deflect, and how does their kinetic energy change while in the region between the plates?"
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url: "https://nerd-notes.com/ubq/117420/"
date_modified: "2026-08-04T06:52:06+00:00"
---

# A velocity selector consists of two horizontal parallel conducting plates producing a uniform downward electric field of magnitude \(E\), and a uniform magnetic field of magnitude \(B\) directed into the page throughout the region between the plates. Positively charged ions of charge \(+q\) enter the region horizontally to the right with speed \(v\). If the ions enter with a speed \(v > \dfrac{E}{B}\), towards which plate do the ions deflect, and how does their kinetic energy change while in the region between the plates?

A velocity selector consists of two horizontal parallel conducting plates producing a uniform downward electric field of magnitude \(E\), and a uniform magnetic field of magnitude \(B\) directed into the page throughout the region between the plates. Positively charged ions of charge \(+q\) enter the region horizontally to the right with speed \(v\). If the ions enter with a speed \(v > \dfrac{E}{B}\), towards which plate do the ions deflect, and how does their kinetic energy change while in the region between the plates?

![A schematic diagram showing two horizontal parallel conducting plates. The upper plate is at a higher electric potential than the lower plate. Uniform vertical arrows between the plates point downward and are labeled E. An array of uniform cross symbols distributed between the plates represents a magnetic field labeled B directed into the page. A particle labeled +q enters horizontally from the left along the central line with a velocity arrow pointing to the right labeled v. No other labels, lines, text, or axes appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1785826325-mK2oYT.jpg)

- **A.** Deflection Direction: Toward the bottom plate | Change in Kinetic Energy: Increases
- **B.** Deflection Direction: Toward the bottom plate | Change in Kinetic Energy: Decreases
- **C.** Deflection Direction: Toward the top plate | Change in Kinetic Energy: Decreases
- **D.** Deflection Direction: Toward the top plate | Change in Kinetic Energy: Increases

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/117420/*