A very long straight wire carries a current I. At the instant when a charge +Q at point P has velocity v, as shown, the force on the charge is (a) along Oy (b) opposite to Oy (c) along Ox (d) opposite to Ox

Answer: (a). IPvF (along Oy)B into page Current flows along +y; at P (to the right of the wire) the right-hand rule gives B into the page ( - z). v is along +x: F = Q v i×(-B k) = QvB j So the answer is (a) along Oy.

A very long straight wire carries a current I. At the instant when a… | NEET 2005 (AIPMT)

Q119NEET 2005 · AIPMTMedium

Moving Charge in a Magnetic Field

A very long straight wire carries a current $I$ . At the instant when a charge +Q at point P has velocity $\vec{v}$ , as shown, the force on the charge is

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Answer: (a)

Current flows along $+y$ ; at P (to the right of the wire) the right-hand rule gives $\vec B$ into the page ( $-\hat z$ ).
$\vec v$ is along $+x$ : $\vec F = Q\,v\hat i\times(-B\hat k) = QvB\,\hat j$
So the answer is (a) along Oy.

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