# Magnetic cone

A hollow cone (like a party hat) has vertex angle $$2\theta$$, slant height $$L$$, and surface charge density $$\sigma$$. It spins around its symmetry axis with angular frequency $$w$$. What is the magnetic field at the tip.

Use $$\theta= 30^\circ , L = 8\text{ m}, \sigma = \dfrac2{\mu_0} , w= 18$$.

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