A magnetic force field exerts a force on a charge in field and these charges in motion constitute an electric current.
If the strength of the magnetic field called flux densityDensity is the measurement of how tightly a material is packed together i.e. how closely the particles are packed in the material. The tighter the material is packed the more its... More can be represented B and the angle between the magnetic field and the direction of the charged motion is θ, when a force\( \scriptsize \overrightarrow{F}\) is applied at velocity v, then,
\( \scriptsize \overrightarrow{F} = q \overrightarrow{V}\overrightarrow{B} sinθ\)F = force in newton
V = average velocity of the charge in ms-1
B = flux induction or magnetic induction in Tesla (T)
q = charge in coulombs
I Tesla =1 weber per m2 wm-2
The expression BVsinθ can be represented as B × V
B × V = BVsinθ
F = qVBsinθ =q (B × B)
When V and B are parallel in the same direction, θ = 0, then F = 0
When V and B are perpendicular, sinθ = sin 90 = 1, then
F = qVB
Example
Find the magnetic force experienced by an electron projected into a magnetic field of flux density 20 Tesla with a velocity of 4 x 106 ms-1 and in a direction of (i) 90° (ii)60° (charge in an electron=1.6 x 10-19 c)
Solution
(i) F = qVB = qVBsinθ
=1.6 x 10-19 x 4 x 106 x 20 x sin 90
= 1.6 x 10-19 x 4 x 106 x 20
= 6.4 x 10-13 x 20
= 1.28 x 10-11 N
(ii) F = qVB sin60
= 1.6×10-19 x 4 x 106 x sin 60
= 6.4 x 10-13 x 20 x 0.866
= 1.28 x 10-11 x 0.866
= 1.11 x 10-11 N
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