Question
An electron is not deflected while passing through any field. Is it possible that there is no magnetic field present at that place? Explain.
✓
Answer
Exerting force in magnetic field on a moving electron with velocity $\vec{v}$
$\overrightarrow{ F }=-e(\vec{v} \times \overrightarrow{ B })$
or $\overrightarrow{ F }=-e v B \sin \theta$
If $\theta=0^{\circ}$ or $180^{\circ}$, the magnitude of force F will be zero. Hence, an electron will not be deflected if it moves parallel or opposite to the direction. So, we cannot say that magnetic field is absent.
$\overrightarrow{ F }=-e(\vec{v} \times \overrightarrow{ B })$
or $\overrightarrow{ F }=-e v B \sin \theta$
If $\theta=0^{\circ}$ or $180^{\circ}$, the magnitude of force F will be zero. Hence, an electron will not be deflected if it moves parallel or opposite to the direction. So, we cannot say that magnetic field is absent.
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