1.

A charged particle, having a charge q, is moving with a speed v along the x-axis. It enters a region of space where an electric field vecE ( = E hatj) and a magnetic field vecB are both present. The particle, on emerging from this region, is observed to be moving along the x-axis only. Obtain an expression for the magnitude of vecB in terms of v and E. Give the direction of vecB.

Answer»

Solution :As the charged particle finally moves undeviated along the x-axis only, it MEANS that force due to electric field and force due to magnetic field are just equal and opposite and are nullifying each other i.e.,
`Q vecE + q vecv xx vecB = vec0 "or" QE = qvB implies B = E/v`
It is POSSIBLE only when `vecB` is along the z-axis. thus, particles, possessing a particular speed .v. only will move undeviated under the INFLUENCE of a pair of crossed electric and magnetic fields.


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