Which one of the following options is correct regarding the typical double-squirrel-cage structure used in induction motors?

The operating region of the developed torque ( $T_{\mathrm{em}}$ ) and speed ( $\omega$ ) of an induction motor drive is given by the shaded region OQRE in the figure. The load torque $\left(T_L\right)$ characteristic is also shown. The motor drive moves from the initial operating point O to the final operating point S . Which one of the following trajectories will take the shortes time?

A three phase, 50 Hz, 6 pole induction motor runs at 960 rpm. The stator copper loss, core loss, and the rotational loss of the motor can be neglected. The percentage efficiency of the motor is

A 10-pole, 50 Hz, 240 V, single phase induction motor runs at 540 RPM while driving rated load. The frequency of induced rotor currents due to backward field is