Question

3. An electron moves with a speed of 2.00×10⁷ ms⁻¹ in an orbit in a uniform magnetic field of 1.20×10⁻³T. Calculate the radius of the orbit. [Mass of an electron=9.11×10⁻³¹kg; charge on an electron=1.61×10⁻¹⁹C]

Accepted Answer

For circular motion in a magnetic field, the magnetic force provides the centripetal force:
qvB = mv²/r ⟹ r = mv/(qB)
r = (9.11×10⁻³¹ × 2.00×10⁷)/(1.61×10⁻¹⁹ × 1.20×10⁻³)
r = (1.822×10⁻²³)/(1.932×10⁻²²)
r ≈ 0.0943m (9.43×10⁻²m)

WAEC Physics 2014 Theory — Question 3

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