Why did rock ''n'' roll, and especially elvis presley, become so popular in the 1950s? what was the role of radio and, later, tv?

Rock n' Roll and Elvis Presley became popular in the 1950s through the rise of counterculture and young peoples desire for something new and rebellious. Elvis' music and rock'n roll more generally signified a shifting tide in American society amongst youth. Youth became interested in upsetting the status quo and listening and being involved in things that were once considered taboo like rock'n roll. Radio and TV helped to spread this music because it provided a medium for people to hear and learn of new artists and music styles quickly. 

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