The correct answer is: A. bus-bars.
A Weston synchronoscope is a device used to synchronize two alternating current (AC) generators or motors. It consists of two coils, a fixed coil and a rotating coil. The fixed coil is connected across the bus-bars, which are the main conductors that carry electricity to the generators or motors. The rotating coil is connected to the incoming alternator, which is the generator or motor that is being synchronized.
When the two coils are connected, the magnetic fields of the coils interact. This interaction causes the rotating coil to turn until it is in line with the magnetic field of the fixed coil. When the rotating coil is in line, the two generators or motors are synchronized and can be operated together.
The other options are incorrect because:
- Option B, incoming alternator, is incorrect because the incoming alternator is connected to the rotating coil, not the fixed coil.
- Option C, a lamp, is incorrect because a lamp is not used in a Weston synchronoscope.
- Option D, none of the above, is incorrect because option A is the correct answer.