Chapter 12 · Physics
Magnetic Effects of Electric Current
Current creates a magnetic field. The module here computes actual field strengths from B = μ₀I/2πr and B = μ₀nI, then draws the field lines at the computed spacing — plus trainers for both of Fleming's rules.
Magnetism Lab — Fields, Motors & Generators
Field magnitude and direction are computed from the standard electromagnetism relations using μ₀ = 4π×10⁻⁷ T·m/A.
- B = μ0I/2πr
- 0.020 mT
- Direction
- Counter-clockwise (viewed from current source), by right-hand thumb rule
Formula sheet
Field near a straight wire
B = μ₀I / 2πr
B is directly proportional to current and inversely proportional to distance.
Field inside a solenoid
B = μ₀ n I
n is turns per metre; the field inside is uniform.
Permeability of free space
μ₀ = 4π × 10⁻⁷ T m A⁻¹
Constant used in both field formulas.
Force on a conductor
F = BIL sinθ
Maximum when the conductor is perpendicular to the field.
Right-hand thumb rule
Thumb = current, curled fingers = field
Gives the direction of circular field lines around a wire.
Fleming's left-hand rule
Forefinger = field, Centre = current, Thumb = force
Used for motors.
Fleming's right-hand rule
Forefinger = field, Thumb = motion, Centre = induced current
Used for generators.