Hi! Can someone explain for #5 why there is no effect on the coil even though th

Question

Hi! Can someone explain for #5 why there is no effect on the coil even though the magentic field has changed?

A loop of wire 5 cm in diameter is hung by cloth thread, and annanged so that it can swing between the poles of an electromagnet as shown in the figure. The plan is that the plane in which the loop swings will be parallel to the plane of the coils that make up the magnet. In the drawing those coils are above and below the plane of this paper. The coil is released from some heighth. The magnetic field which is 0.3 T, is confined to the region between the electromagnets, so that at the original time when the loop is released it is experiencing no field, and remains so until it enters the region between the magnets. Where there is a field, it is spatially uniform 1. When the ring enters the magnetic field (A) it will speed up (B) it will slow down (C it is unaffected since it is not in a circuit (D) it wi bounce back D2 2. Which is true? (A) There will be a clockwise current induced in the loop hen it enters the magnetic field (B) There will be a counter-clockwise current induced in the loop when it enters the magnetic field (C) No current is induced in the loop (D There will be a clockwise current induced in the loop first when it enters the field, that then reverses as the loop begins to rise (B)There will be a when that then reverses as the loop begins to rise counterclockwise current induced in the loop it enters the field, 3. If the loop twists as it descends so that it is no longer going straight across the face of the electromagnet, (making it look more elliptical as we see it) what happens to the flux through the loop? (A) It increases because the angle changes. (B) It decreases because the field changes (C Itincreases because the area changes (D) Itdecreases because the angle changes (E) It stays constant. 4. Which is true as the loop swings into the region of the field? (A) A current is induced in the wire that creates a field pointed out of the page (B) A current is induced in the wire that creates a field pointed into the page (C A current is induced in the wire that creates a field pointed to the right (D) A current is induced in the wire that creates field pointed to the left (E) No current is induced in the field 5. Suppose I were to reverse the polarity of the electromagnet just as the coil enters the field. After the polarity is reversed, (A) the coil will reverse its direction (B) the coil will speed up (C the coil will behave just as it did before the polarity was reversed (D) the coil will immediately stop. (E the coil will flip over.

Explanation / Answer

When polarity changes, direction of induced current also changes. And so force on the loop due to magnetic field vectors acts again on it in the upward direction. So there will be no effect of change in polarity.

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