Question

what do you mean by reversing the polarities of batteriesand how it's done?

Answer 1

The reversing of polarities of battery is done when we interchange the positive terminal of the battery with negative terminal of the battery keeping the battery same . actually we horizontally invert the battery so that the positive terminal is replaced by its negative terminal and the negative terminal is replaced by positive terminal . we do not change the battery and hence the emf will be same .