The only way I can imagine getting these readings is if something is wrong with the circuit. If the circuit is off, then you get 0v on each of the readings, of course.
In any case, if you are getting the readings as you describe, you have an electrical problem that will require a competent electrician to solve.
How does the voltage measured across a dry cell ompare with the voltage drop measured across three bulbs in series?
The voltage measured across an open in a series circuit is the equivalent of the sourse voltage.
The full circuit voltage
A grounded neutral will be at earth potential. A floating neutral will be at a voltage dependent upon the voltage imbalance between phases, and the design of the transformer.
It's measured with an AC voltmeter.
The current is the amperage. It is measured in series. Voltage is measured across the line (parallel).
transformer
1.5V if measured across the + and - terminals, otherwise 0V. When measured at points with identical potential (voltage), there is no difference between voltage levels and no current flows.
It could be anything from zero to a million volts.
It shouldn't. The open end of a non connected neutral should have the same potential as the voltage feeding the circuit. The only time a voltage will show is when the return neutral is tested with a meter to the neutral bar or the ground return bar. It will then show what the supply voltage to the connected load is. Once this neutral is connected to the neutral bar there will be no voltage shown across the test meter between the neutral and the neutral bar or the ground bar.
No one is going to be able to tell you that. You are looking for the measured voltage, so go and measure it. In any case, if you were just looking for the voltage it will depend on the circuit current. You can work it out using ohms law (Voltage = Current * Resistance).
In North America the neutral wire is never fused. This is because of the three wire circuit that uses a common neutral. If there are two loads connected across a common neutral circuit and the neutral opens a 230 volt supply will be impressed across both loads as they are now in series with the supply. If both loads were balanced then the voltage drop across both loads would be equal. Dropping 120 volts across each load. Where the problem arises is if the two loads are not balanced and voltage drop goes higher than the manufactures recommended voltage, then the connected device could burn out.