This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
A Java 'char' is 16 bits, or two bytes, in length, so yes.
Does a single 'char' translate to two bytes when written to a file? That depends entirely on the encoding in use. If the encoding is iso-latin or UTF-8 (which are very common here in the US) then all the alphanumeric characters used in English will be written to a file as a single byte per character.