Final answer:
The RCCR points in a 12V generator system close when the coil is rotated one-fourth of a revolution, leading to the magnetic flux changing from maximum to zero and inducing an emf. The Right-Hand Rule-1 (RHR-1) shows that the emfs in a generator loop are in the same direction, thereby adding up.
Step-by-step explanation:
The RCCR points in the 12V generator system close at the moment when the generator coil has rotated one-fourth of a revolution, which causes the magnetic flux through the coil to change from its maximum to zero, consequently inducing an emf (electromotive force). To understand why the emfs in the sides of the generator loop add up rather than cancel each other out, we can use the Right-Hand Rule (RHR-1), which states that if the thumb of your right hand points in the direction of the magnetic field, and your fingers point in the direction of the motion of the wire, then the force (emf) is directed out of the palm. For a generator loop, when placing your right hand accordingly, you'll find that the induced emfs in the two sides of the loop are indeed in the same sense (direction), which means they add together.