What were Nikola Tesla's contributions to physics?
He was the father of many fields in physics. But to understand his contribution to science or physics you need to study his original lectures, patents and writings because young fellows of science do not even know that Nikola Tesla was the greatest physicist of all time.
The newspapers called him the wizard of electricity and even the professionals were wondering seeing his demonstrations. During his lectures he explained everything about his researches and findings wich accomplishments or outcomes were later credited to others but in reality they originated from or belonged to Nikola Tesla.
And just to give an approcimately clear answer:
He discovered the particle electron, cosmic and solar neutrino radiation, one wire longitudinal/torsion transmission of electrical and mechanical energy, high frequency currents, resonant energy conversion, telegeodinamics, desintegration and transmutation of elements, the working of gravity etc.
It is hard to distinguish his work as a physicist and his work as inventor because he made this two different activities of course simultaneously. But he was also the first who:
Contributed to or invented polyphase generation and transmission of electrical energy, AC motors, high voltage high frequency currents, resonant transformer, remote control and robotics, energy saving lighting, vacuum impregnation, high voltage vacuum pumping, electrical and mechanical theraphy, measuring the parameter of the earth and sun, radio-astronomy, fluid mechanics, ball lightning, electrical soliton wave, renewable energy technologies etc.
For more information please see this short summary about his work:
Nikola Tesla's Life And Work
He wasn't actually very educated in physics, but his contributions were so many, you really should just watch some documentaries on tesla. they are too numerous.
keep in mind that many people took credit for his work and inventions, but history has set the record straight.