There are many sources, I have looked into it a number of times over the course of years, so to name just one now would be impossible, but if you look to Catholicism itself, how they define it, ex cathedra means when the pope speaks "infallibly," which they have also defined, and to speak such he is in effect proclaiming dogma/doctrine that his followers are obliged to accept, because they essentially claim he cannot be wrong in making such a proclamation.
Ex cathedra is a Latin phrase which means "from the chair." It refers to binding and infallible papal teachings which are promulgated by the pope when he officially teaches in his capacity of the universal shepherd of the Church a doctrine on a matter of faith or morals and addresses it to the entire world. http://www.catholic.com/quickquestions/what-does-the-term-ex-cathedra-mean-and-where-did-the-catholic-church-come-up-with-it
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Ex Cathedra, literally "from the chair", a theological term which signifies authoritative teaching and is more particularly applied to the definitions given by the Roman pontiff. Originally the name of the seat occupied by a professor or a bishop, cathedra was used later on to denote the magisterium, or teaching authority. The phrase ex cathedra occurs in the writings of the medieval theologians, and more frequently in the discussions which arose after the Reformation in regard to the papal prerogatives. But its present meaning was formally determined by the Vatican Council, Sess. IV, Const. de Ecclesia Christi, c. iv: "We teach and define that it is a dogma Divinely revealed that the Roman pontiff when he speaks ex cathedra, that is when in discharge of the office of pastor and doctor of all Christians, by virtue of his supreme Apostolic authority, he defines a doctrine regarding faith or morals to be held by the universal Church, by the Divine assistance promised to him in Blessed Peter, is possessed of that infallibility with which the Divine Redeemer willed that His Church should be endowed in defining doctrine regarding faith or morals, and that therefore such definitions of the Roman pontiff are of themselves and not from the consent of the Church irreformable." http://www.catholic.com/encyclopedia/ex-cathedra
Care to read up on infallibility?
http://www.catholic.com/encyclopedia/Infallibility
This site teaches fairly thoroughly on Roman Catholic errors:
http://www.bible.ca/catholic-doctrine.htm