Electric motor load vs efficiency historical background

[m_p_w]

Is there a physicist who has discovered this, and could you explain how he/she did it?
I was trying to find it on the internet, but it only gives me a lab review of load vs efficiency.

thank you

 

[m_p_w]

What I am trying to say is that:
when you increase the load of the electric motor the efficiency goes up (it creates this sqr(x) function, so the maximum efficiency is around 75% of rated load). But my question is this:
Was there a physicist who have observed this phenomena and described it if this is the case then what was his name and how he did this? or is this based on a theory; therefore, people knew this from the beginning of the creation of this particular theory, and if this is the case then what is the name of the theory, and how he came up with this theory?

 

[m_p_w]

nevermind about this question