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# Magnetic field Q watch

1. the answer to part b) is eE = Bev so therefore E=Bv and v=E/B

Why is this the answer? I am confused..

Thanks
2. It will only continue in a straight line when the resultanf=t force on it is zero.

ie the electric and magentic forces are equal and opposite.
3. (Original post by teachercol)
It will only continue in a straight line when the resultanf=t force on it is zero.

ie the electric and magentic forces are equal and opposite.
Thanks! PRSOM
4. Referring to the equation: isn't it also because the the forces by the magnetic and electric field are in opposite directions (and equal magnitude), so F=Eq (E field force) and F=Bqv (mag field force) need to be the same. Charge is electron so q=e so Ee=Bev.

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