किस प्रकार की एसी आर्मेचर वाइंडिंग में अलग-अलग आयामों की कुंडलियाँ एक ही सामान्य केंद्र को साझा करते हुए एक दूसरे के भीतर व्यवस्थित होती हैं?

What is the coupling field commonly used between electrical and mechanical systems in electromechanical energy conversion devices?

In a DC shunt motor operating at rated voltage, if the field flux is reduced to 70% of its nominal value while keeping the armature current constant, the percentage increase in speed (assuming negligible armature reaction) is approximately __________.