Switching polarity has no effect on induced emf and current. Hence, there is no effect on the brightness of the bulb.
However, changing the polarity changes the direction of deflection on the voltmeter to the opposite direction.
You can switch the polarity of the bar magnet by clicking on the button with the bar magnet and two semi-circular arrows on the bottom right. Note how the positions of the north and south poles are switched every time you click on this button.
Drag the bar magnet from left to right through the top coil, then repeat the same process after switching the polarity of the magnet. What effect, if any, does switching the polarity have on the brightness of the bulb and the needle of the voltmeter?
a) Switching the polarity of the magnet has no effect on the bulb brightness, but inverts the order of the needle deflection in the voltmeter.
b) Switching the polarity of the magnet has no effect on either the bulb brightness or the voltmeter.
c) Switching the polarity of the magnet changes the average brightness of the bulb but has no effect on the voltmeter.
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Based on our data, we think this problem is relevant for Professor Buchholz's class at California Baptist University.