At the midpoint of a finite solenoid of length L, radius R, turn density n and current I, the axial magnetic field is:
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Question

At the midpoint of a finite solenoid of length L, radius R, turn density n and current I, the axial magnetic field is:

G1 Physics · Accepted Answer

For a finite solenoid, B=(μ₀nI/2)(cosθ₁+cosθ₂). At the midpoint the two cosines are equal to (L/2)/√(R²+(L/2)²), giving the stated result.