Question

An alpha particle is projected vertically upward with a speed of 3.0 × 10⁴ km s⁻¹ in a region where a magnetic field of magnitude 1.0 T exists in the direction south to north. Find the magnetic force that acts on the α-particle.

Answer 1

Given:
Upward speed of the alpha particle, v = 3 × 10⁴ km/s = 3 × 10⁷ m/s
Magnetic field, B = 1.0 T
The direction of the magnetic field is from south to north.
Charge of the alpha particle, q = 2e,
where e is the charge of an electron.
q = 2 × 1.6 × 10⁻¹⁹ C,
Magnetic force acting on the α-particle,
$\overrightarrow{F}=q\overrightarrow{v}\times \overrightarrow{B}\sin 90°$
= 2 × 1.6 × 10⁻¹⁹ × 3 × 10⁷ × 1
= 9.6 × 10⁻¹² N, towards west

The direction of magnetic force can be found using Fleming's left-hand rule.