Apparent power is defined as the product of the RMS voltage and RMS current, without regard to the phase angle between them. That gives S in volt-ampere (VA). So the expression that matches this definition is V × I in VA. Real power, the actual work done, is VI cos(phi) and is measured in watts, while reactive power is VI sin(phi) in VAR. The other descriptions either mix in the cos(phi) or use the wrong unit, or rely on current and resistance, which isn’t how apparent power is defined.

Induction motors are categorized by how their rotor is built, which determines how torque is produced and how the motor starts and runs. The two main rotor designs are the squirrel-cage rotor and the wound rotor (round wound). In a squirrel-cage rotor, conductive bars are embedded in the rotor surface and shorted by end rings, forming a closed "cage." The stator’s rotating magnetic field induces currents in these bars, generating torque without any electrical connection to the rotor. This design is simple, rugged, inexpensive, and requires little maintenance, which is why it’s the most common type. A wound rotor has windings on the rotor connected to external circuitry through slip rings. By inserting resistors or other control devices in that circuit, you can tailor the rotor resistance, giving high starting torque and adjustable speed control—useful in heavy-load starts or precise drive applications, but it is more complex and costly due to the brushes and rings. The other choices don’t fit because they describe power supply (DC vs AC), motor behavior (synchronous vs asynchronous), or physical components (rotor vs stator) rather than the rotor construction that defines the main classes of induction motors.

Short circuit current is typically greater. When a fault creates a path with almost zero impedance, the current is determined mainly by the source voltage and this very small impedance, so the current can surge far above normal operating levels (I ≈ V/Z, with Z very small). Overload current, by contrast, is simply current that goes beyond what the circuit is designed to carry and is limited by the circuit’s impedance and protection settings, so it stays much closer to the normal operating current. This is why protection devices are designed to interrupt the much larger fault (short-circuit) currents to prevent damage.

Short-circuit current is the surge that happens when a fault creates a path of very low resistance, so the current rises well above the normal operating level. Because the path is low resistance and not the intended conductor route, the current isn’t confined to the normal conducting paths. This distinguishes it from normal overloads that still flow within the designed circuit paths. The other descriptions either imply the excess current stays in the usual conductors, or they refer to fuse ratings (voltage or continuous current) rather than the behavior of current during a fault.