NapkinCalc

Physics 3 — Electricity & Magnetism

Making fields: the solenoid

continues from lesson 3 — values defined earlier in the course stay live here

ELI5: wrap wire into a tight coil and the current creates a uniform field inside: B = μ₀·n·I. More turns per metre or more current → more field. That coil is the electromagnet, the relay, the MRI bore.

μ0=4⋅π⋅10−7\mu_{0} = 4 \cdot \pi \cdot 10^{-7} = 1.2566×10−61.2566 \times 10^{-6} permeability of free space (T·m/A)
nturns=2000n_{turns} = 2000 turns per meter
Icoil=5I_{coil} = 5 current (A)
Bsol=μ0⋅nturns⋅IcoilB_{sol} = \mu_{0} \cdot n_{turns} \cdot I_{coil} = 0.01260.0126 field inside (T)

Try it yourself: a solenoid with 1000 turns/m carries 3 A. What is the field inside? (B = μ₀·n·I; μ₀ is mu_0 above.)

Byou=μ0⋅1000⋅3B_{you} = \mu_{0} \cdot 1000 \cdot 3 = 0.00380.0038 ✏️ Your turn: compute μ₀ · 1000 · 3 (reuse mu_0 defined above).
✓ pass abs(Byou−μ0⋅1000⋅3)<10−9\mathrm{abs}\left(B_{you} - \mu_{0} \cdot 1000 \cdot 3\right) < 10^{-9} green when your solenoid field is correct