A negative test charge is moving near a long straight wire carrying a… | JEE Main 2017 (9 Apr, Shift 1)

Q95JEE Main 2017 · 9 APR · SHIFT 1Medium

Moving Charge in a Magnetic Field

A negative test charge is moving near a long straight wire carrying a current. The force acting on the test charge is parallel to the direction of the current. The motion of the charge is:

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Answer: (b)

Take the current along $+\hat z$ and the charge at $+\hat x$ from the wire; there $\vec B$ is along $+\hat y$ .
$\vec F = q(\vec v\times\vec B)$ with $q<0$ ; for $\vec F$ along $+\hat z$ we need $\vec v\times\hat y$ along $-\hat z$ .
$(-\hat x)\times\hat y = -\hat z$ , so $\vec v$ is along $-\hat x$ , i.e. towards the wire.
So the answer is (b) towards the wire.

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Moving Charge in a Magnetic Field question from JEE Main 2017 (9 Apr, Shift 1)

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