• http://www.pbs.org/tesla/ll/index.html
  
• http://engineering.mit.edu/ask/what%E2%80%99s-difference-between-ac-and-dc
  
• http://www.teslasociety.com/biography.htm
  
• http://www.pbs.org/newshour/rundown/5-things-you-didnt-know-about-nikola-tesla/
  
• http://science.howstuffworks.com/innovation/famous-inventors/famous-nikola-tesla-inventions1.htm