The drawing shows the uniform magnetic field inside a long, straight solenoid. The field is directed into the plane of the drawing, and is increasing.What is the direction of the electric force on a positive point charge placed at point "b"?Select one:a.misleading question — the electric force at this point is zerob.To the rightc.To the leftd.Straight upe.Straight downClear my choice
Question
The drawing shows the uniform magnetic field inside a long, straight solenoid. The field is directed into the plane of the drawing, and is increasing.What is the direction of the electric force on a positive point charge placed at point "b"?Select one:a.misleading question — the electric force at this point is zerob.To the rightc.To the leftd.Straight upe.Straight downClear my choice
Solution
According to Faraday's law of electromagnetic induction, a changing magnetic field will induce an electric field. The direction of the induced electric field will be such that it creates a current (or moves a positive charge) in a direction that opposes the change in the magnetic field.
In this case, the magnetic field is directed into the plane of the drawing and is increasing. The induced electric field will therefore be in a direction that opposes this increase.
In a solenoid, the induced electric field forms circular loops around the axis of the solenoid. If we use the right-hand rule, with the thumb pointing in the direction of the magnetic field (into the plane of the drawing), the fingers will curl in the direction of the induced electric field.
For a positive charge at point "b", the electric force will be in the same direction as the electric field.
Therefore, the direction of the electric force on a positive point charge placed at point "b" will be to the left.
So, the correct answer is (c) To the left.
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