Plain-English Meaning
A long straight wire carrying current I produces a circular magnetic field whose strength falls off as 1/r.
Keep charge, field, potential, and current distinct. That single habit fixes a large fraction of electromagnetism errors.
Deeper Explanation
A long straight wire carrying current I produces a circular magnetic field whose strength falls off as 1/r.
Worked Example
Problem: Find B 0.05 m from a wire carrying 10 A. (μ₀ = 4π×10⁻⁷ T·m/A)
- B = μ₀I/(2πr)
- B = (4π×10⁻⁷ × 10)/(2π × 0.05)
- B = (4×10⁻⁶)/(0.1) = 4×10⁻⁵ T
Result: B = 4×10⁻⁵ T = 40 μT
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At A Glance
Category: Electromagnetism
Levels covered:
Best use: Start with the formula meaning, then move to the worked example and quiz so the equation turns into a tool instead of a memorised line.