As an opening, you may wish to point to something striking about radio and television. One remark about the media--which was only newspapers in his time--was made by Napoleon Bonaparte who said that the first action to take after conquering a country was to get control of the newspapers. Whoever controls the media, controls the dissemination of information in its every aspect. When the visual was added to the media, an entirely different dimension was added.
The most memorable contrast between the radio and the television as influential media in the United States occurred during the 1960 presidential campaign of Richard Nixon and John F. Kennedy. After radio programs and other campaigning, Nixon was ahead 11 points in the national polls. In September of 1960 after the first Presidential Debates, which historians record as the "turning point" of the election, was broadcast on television, John F. Kennedy's approval rate in the polls soared; he was elected President of the United States in less than two months after this debate.