It is seen that in the first half of the revolution current flows always along ABLMCD i.e. brush no 1 in
contact with segment ‘a’. In the next half revolution, in the figure the direction of the induced current in
thecoil is reversed. But at the same time the position of the segments a and b are also reversed which
results that brush no 1 comes in touch with the segment b. Hence, the current in the load resistance again
flows from L to M. The waveform of the current through the load circuit is as shown in the figure. This
current is unidirectional.
This is basic working principle of DC generator, explained by single loop generator model. The position
of the brush of DC generator is so arranged that the changeover of the segments ‘a’ and ‘b’ from one
brush to other takes place when the plane of rotating coil is at right angle to the plane of the lines of force.
It is so become in that position, the induced emf in the coil is zero.