Three points P, Q

PHYSICS · Single correct · A Level · Physics · Fields and their consequences · Fields and their consequences

Problem

Three points P, Q, and R lie at radial distances 2 cm2\,\text{cm}, 4 cm4\,\text{cm}, and 6 cm6\,\text{cm}, respectively, from the axis of a long, straight wire that carries a constant current. Which ranking correctly orders the magnitudes of the magnetic field at the three points from greatest to least? (a) BP>BR>BQB_{\text{P}} > B_{\text{R}} > B_{\text{Q}} (b) BP>BQ>BRB_{\text{P}} > B_{\text{Q}} > B_{\text{R}} (c) BR>BQ>BPB_{\text{R}} > B_{\text{Q}} > B_{\text{P}} (d) BQ>BP>BRB_{\text{Q}} > B_{\text{P}} > B_{\text{R}}

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