Question
15) A magnetic field B is applied through a coil in a direction perpendicular to the plane of the coil as shown.
Use Faraday's law and Lenz's law to state and explain the direction of the induced current through resistor R when the magnetic field B is decreasing. [4]
Answer
When the magnetic flux density B decreases, the magnetic flux linkage of the coil into the page, given by the formula ϕ = B A, decreases. By Faraday's Law of electromagnetic induction, there will be an induced e.m.f. produced in the coil.
This induced e.m.f. in the coil will cause an induced current to flow.
By Lenz's law, since the magnetic flux linkage into the page has deceased, the induced current will produce magnetic flux into the page. According to the right hand grip rule, the induced current will flow in the clockwise direction as shown below.
Therefore, the current will flow through the resistor from the right to the left.