Positron Helix Around Current-Carrying Wire · Physics Brawl 2019 #FoL.19

Physics · electromagnetism

Problem

A positron is moving at a distance R=10R = 10 cm from a wire carrying a current I=2.5I = 2.5 A. The current generates a magnetic field, which causes the positron to orbit around the wire. The component of the positron's velocity in the direction of the current is v∥=1.5v_{\parallel} = 1.5 m·s⁻¹ and the radial component is zero. Under the condition that the movement is stable, determine the period of the positron's orbit around the wire (in milliseconds). Let e=1.6⋅10−19e = 1.6 \cdot 10^{-19} C, μ0=4π⋅10−7\mu_0 = 4\pi \cdot 10^{-7} N·A⁻², me=9.1⋅10−31m_e = 9.1 \cdot 10^{-31} kg.

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