A 3-phase induction motor runs at almost 50 rpm at no load and 25 rpm at full load when supplied with power from a 50 Hz, 3-phase supply. What is the corresponding speed of the rotor field with respect to the rotor?

• A. 25 revolution per minute
• B. 20 revolution per minute
• C. 10 revolution per minute
• D. 30 revolution per minute