no
120 volts
You don't.
yes 240volts is 240 volts
A 50 watt bulb designed to run on 12 volts takes 4.17 amps. A 50 watt bulb designed to run on 230 volts takes 0.217 amps.
Yes you can run a 400 volt heater on 230 volts but you will not get the full wattage rating that the heater produces at 400 volts.
Depends on the size of the circuit which you did not list.
I believe that you can't use New Zealand household electric appliances in the US without adaptations. The residential voltage/Frequency (Hz) in New Zealand is 130V/50 Hz while in US it is 120V/60 Hz <<>> The voltage in New Zealand is 230 volt 50Hertz. The voltage in North America is 120/240 volts at 60 Hertz. A totally resistive appliance will operate fine on the 240 volt portion of the 120/240 volt system. Any appliances that have a motor to operate will not work as efficiently. A 50 Hertz motor on a 60 Hertz system will overheat and run slower. Many appliances use synchronous timer motors for control of the larger appliances. The timing of the appliance will be thrown off as the timers will run faster due to the appliances design to operate only on 50 Hertz.
No a 230 volt appliance should not be pluuged into a 110 volt socket (And vice versa) you need to buy a converter that can be plugged into the 110 volt outlet then the appliance can be plugged into the converter.
Depends on length. The more length, the more resistance.
Definitely not !! it would be dangerous to use 120 volt equipment on a 230 volt supply, it would either blow the fuse or blow up . . You need a transformer to convert 230 volts to 120 volts, and you need one of the right rating. For a washing machine that might be quite a big transformer. We have 110 volt transformers for power tools but they are not big enough.
The appliance should be marked with the correct voltage range, and the voltage applied must lie within this range. Otherwise it might be dangerous.