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If an electron is not deflected in passi...

If an electron is not deflected in passing through a certain region of space can we be sure that there is no magnetic field in that region?

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No, electron would not be deflected if `vecv` and `vecB` are in the same direction. Further the electron would not be delfected if in addition to magnetic field, there is electric field present. THe two deflecting forces may cancel the effect of each other, giveing net Lorentz Force zero.
i.e. `qvecE+q(vecvxxvecB)=0`
If both `vecE` and `vecB` are present then `vecv` and `vecB` can make any angle between them but the `vecE` should be perpendicular both to `vecv` and `vecB`. As a special case you can say that all three velotors should be perpendicular for no deflection of the charge.
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