When iron filings are sprinkled on a cardboard through which a current-carrying wire passes vertically, they…

Question

When iron filings are sprinkled on a cardboard through which a current-carrying wire passes vertically, they arrange themselves in a pattern around the wire. (i) What shape does this pattern take, and what does it indicate about the direction of the magnetic field? (ii) The spacing between adjacent rings increases as we move away from the wire — what does this tell you about the magnetic field at those points?

Accepted Answer

## Model Answer (i) Iron filings arrange in **concentric circles** around the wire, indicating that the magnetic field lines form closed loops around a current-carrying straight conductor. (ii) Wider spacing between rings shows the magnetic field **decreases (weakens)** as distance from the wire increases. *Source: Chapter 12, Section 12.2.1* --- ## Explanation Since this is 1 mark, examiners expect only the key terms: **concentric circles** for part (i) and **field decreases with distance** for part (ii). Avoid lengthy explanations. The passage explicitly states rings grow larger farther away, meaning field lines are less crowded = weaker field — this is the core point to mention.

Science (086) — AI-generated practice question