JEE Main 2017 · 9 Apr · Shift 1 · Physics Q18

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PhysicsSingle correct+4 / -1Question 18 of 90

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 :

away from the wire

towards the wire

parallel to the wire along the current

parallel to the wire opposite to the current

Answer and worked solution

Official answer: B

Take the current along +z and the charge on the +x side, where $\vec B$ is along +y. For $\vec F=q\vec v\times\vec B$ to point along +z with $q<0$ , $\vec v\times\vec B$ must point along −z, which needs $\vec v$ along −x: towards the wire.

Topics:Force on a moving charge

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JEE Main 2017 · 9 Apr · Shift 1, Physics question 18