Magnetic Fields of Conductors & Solenoids — A/L Physics

What must I remember about Magnetic Fields of Conductors & Solenoids?

• Biot-Savart Law: Magnetic field element dB generated by current element I dl at displacement r: dB = (μ0 / 4π) * [(I dl × r̂) / r²] = (μ0 / 4π) * [(I dl sin θ) / r²], where permeability of free space μ0 = 4π × 10⁻⁷ T·m/A.
• Ampère's Circuital Law: Line integral of magnetic field B around ANY closed path equals μ0 times the net steady current enclosed: ∮ B · dl = μ0 I_enclosed.
• Long Straight Conductor: Magnetic field at distance r from infinite straight wire: B = (μ0 I) / (2π r); field lines form concentric circles centered on wire (Right-Hand Grip Rule).
• Solenoids & Toroids: Long tightly wound solenoid of n turns per unit length (n = N / L): Magnetic field inside is uniform and axial: B = μ0 n I; Toroid (doughnut solenoid of mean radius r): B = (μ0 N I) / (2π r).

Test yourself (1 minute)

1. Force between two long parallel conductors

   Magnetic force per unit length between two infinite wires separated by distance d carrying currents I1 and I2: F / L = (μ0 I1 I2) / (2π d); currents in SAME direction ATTRACT; currents in OPPOSITE directions REPEL.

2. Formal SI Definition of Ampere

   The Ampere is that constant current which, maintained in two straight parallel conductors of infinite length and negligible cross-section placed 1 meter apart in vacuum, produces between them a force equal to 2 × 10⁻⁷ N per meter of length.

3. Circular Loop Center Field

   At the center of a circular coil of N turns and radius R: B = (μ0 N I) / (2 R).

Practise Magnetic Fields of Conductors & Solenoids questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 8: Electromagnetism

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Where does Magnetic Fields of Conductors & Solenoids fit in the syllabus?

Unit 8.2 · Year 2 · Term 1