An electron makes 3 × 10⁵ revolutions per second in a circle of radius 0.5 angstrom. Find the magnetic field B at the centre of the circle.
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An electron makes 3 × 10⁵ revolutions per second in a circle of radius 0.5 angstrom. Find the magnetic field B at the centre of the circle.

G1 Physics · Accepted Answer

The revolving electron is equivalent to current I=ef. Therefore B=μ₀ef/(2r). With e=1.6×10⁻¹⁹ C, f=3×10⁵ s⁻¹ and r=0.5 Å, B≈6×10⁻¹⁰ T. Hence A.