A positive charge q is initially at rest at radius r

Question

A positive charge q is initially at rest at radius r<R inside a region where a uniform +z magnetic field increases as B=kt. Neglect the magnetic force during the infinitesimal initial interval. Which statements are correct?

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G1 Physics · Accepted Answer

The induced electric field is tangential with magnitude kr/2, so the initial electric force is qkr/2 tangentially. Its circulation opposes the increasing magnetic flux.