A very long straight wire carries current I. At an instant, a positive charge +Q at point P moves with velocity v⃗ as shown in the diagram. What is the direction of magnetic force on the charge? [Image]
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Question

A very long straight wire carries current I. At an instant, a positive charge +Q at point P moves with velocity v⃗ as shown in the diagram. What is the direction of magnetic force on the charge? [Image]

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G1 Physics · Accepted Answer

Step 1: A current in a long straight conductor produces concentric magnetic field lines; determine local B⃗ by the right-hand grip rule. Step 2: The magnetic force on positive Q moving with velocity v⃗ is F⃗=Q(v⃗×B⃗). Step 3: For the directions drawn at P, v⃗×B⃗ points along +y. Final A. Final answer: (A) along y.