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Rotating Field Generator
AC generators are very efficient as the energy losses are less. Due to sparking and other losses like copper, eddy current, mechanical, and hysteresis losses DC generators are less efficient. In an AC generator, the electrical current reverses direction periodically.
DC power is significantly more energy efficient than AC power. DC motors and appliances have higher efficiency and power to size characteristics. DC-based lighting (LED) is as much as 75% more efficient than incandescent lighting.
220 volt a.c. means the effecitve or virtual value of a.c. is 220 volt, i.e., Ev=220 volt. But 220 volt d.c. has the same peak value (i.e., 220 volt only). Moreover, the shock of a.c. is attractive and that of d.c. is repulsive. Hence 220 volt a.c. is more dangerous than 220 volt d.c.
The voltage and frequency of alternating current (AC) electricity used in homes varies from country to country throughout the world. Typically, either 110-volt AC (110V) or 220-volt AC (220V) is used. Most countries use 50Hz (50 Hertz or 50 cycles per second) as their AC frequency. Only a handful use 60Hz.
Now resistance in AC (also known as impedance) It means AC is more dangerous than DC in case when human body act as a capacitor. In short, the impedance and resistance in DC is lower than AC as it decreases when frequency increases. This way, AC is more harmful than DC.
12 volts DC is not a shock hazard. You can’t touch the wires in your 120V AC household electrical system without getting a nasty, dangerous shock, but you can touch bare wires carrying 12V DC in your car, even lay your hands across the positive and negative 12V battery terminals, without risk of electrocution.