The four stator conductors (A, A$'$, B and B$'$) of a rotating machine are carrying DC currents of the same value, the directions of which are shown in the figure (i). The rotor coils $a$–$a'$ and $b$–$b'$ are formed by connecting the back ends of conductors $a$ and $a'$, and $b$ and $b'$, respectively, as shown in figure (ii). The e.m.f. induced in coil $a$–$a'$ and coil $b$–$b'$ are denoted by $E_{a\text{–a'}$ and $E_{b\text{–}b'}$, respectively. If the rotor is rotated at uniform angular speed $\omega \, \text{rad/s}$ in the clockwise direction then which of the following correctly describes the $E_{a\text{–}a'}$ and $E_{b\text{–}b'}$?}
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