An electron enters perpendicularly into a uniform magnetic field which has a flux density of 0.12 T This results in a magnetic force of 9.6 x 10\(^{-2}\) N ...

Assessment: WAEC SSCE - Physics - 2016 (Essay) Subject: Physics

Question 1 Report

An electron enters perpendicularly into a uniform magnetic field which has a flux density of 0.12 T This results in a magnetic force of 9.6 x 10\(^{-2}\) N on the electron. Calculate the speed of the electron as it enters the magnetic field. (e =1.6 x \(10^{19}\) C)

Answer Details

An electron moving perpendicular to a uniform magnetic field experiences a force

\[F=Bev\sin\theta,\qquad \theta=90^\circ,\ \sin 90^\circ=1.\]

Making the speed the subject:

\[v=\frac{F}{Be}.\]

Substituting \(F=9.6\times10^{-12}\text{ N}\), \(B=0.12\text{ T}\) and \(e=1.6\times10^{-19}\text{ C}\):

\[v=\frac{9.6\times10^{-12}}{0.12\times1.6\times10^{-19}}=\frac{9.6\times10^{-12}}{1.92\times10^{-20}}=5.0\times10^{8}\text{ m s}^{-1}.\]

The speed of the electron as it enters the field is \(5.0\times10^{8}\text{ m s}^{-1}\).

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