---
title: "A long straight wire lies perpendicular to the page and carries a constant electric current \\(I\\) directed out of the page. Point \\(P\\) is located at a distance \\(d\\) to the right of the wire, and point \\(Q\\) is located at a distance \\(2d\\) to the left of the wire. Which of the following correctly indicates the direction of the magnetic field at point \\(P\\) and the ratio of the magnetic field magnitude at point \\(P\\) to that at point \\(Q\\), \\(B_P/B_Q\\)?"
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url: "https://nerd-notes.com/ubq/117472/"
date_modified: "2026-08-04T06:52:16+00:00"
---

# A long straight wire lies perpendicular to the page and carries a constant electric current \(I\) directed out of the page. Point \(P\) is located at a distance \(d\) to the right of the wire, and point \(Q\) is located at a distance \(2d\) to the left of the wire. Which of the following correctly indicates the direction of the magnetic field at point \(P\) and the ratio of the magnetic field magnitude at point \(P\) to that at point \(Q\), \(B_P/B_Q\)?

A long straight wire lies perpendicular to the page and carries a constant electric current \(I\) directed out of the page. Point \(P\) is located at a distance \(d\) to the right of the wire, and point \(Q\) is located at a distance \(2d\) to the left of the wire. Which of the following correctly indicates the direction of the magnetic field at point \(P\) and the ratio of the magnetic field magnitude at point \(P\) to that at point \(Q\), \(B_P/B_Q\)?

![A schematic diagram showing a cross section of a current-carrying wire and two observation points. At the center is a circle with a small filled dot inside, labeled '\(I\)'. A horizontal dashed reference line passes through the center of the circle. To the right of the circle along the reference line, a filled dot is labeled '\(P\)'. A horizontal dimension line below the reference line extends from the circle to point \(P\), labeled '\(d\)'. To the left of the circle along the reference line, a filled dot is labeled '\(Q\)'. A horizontal dimension line below the reference line extends from the circle to point \(Q\), labeled '\(2d\)'. No other labels, lines, text, or axes appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1785826335-4qUryR.jpg)

- **A.** Direction at \(P\): Toward the bottom of the page | Ratio \(B_P/B_Q\): \(1/2\)
- **B.** Direction at \(P\): Toward the bottom of the page | Ratio \(B_P/B_Q\): \(2\)
- **C.** Direction at \(P\): Toward the top of the page | Ratio \(B_P/B_Q\): \(1/2\)
- **D.** Direction at \(P\): Toward the top of the page | Ratio \(B_P/B_Q\): \(2\)

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/117472/*