When I was a kid in the 1950s, I was interested in rockets to the moon and I had a tiny toy rocket. It did not fly. In fact it was not a rocket at all, it was a radio. It had a geranium diode inside and a rod, connected to a wire coil, sticking out the top. Moving the rod in and out tuned in AM radio stations. It used no batteries and obtained a weak signal that one listened to with an earphone. See illustration on left.
Earlier radios, in the 1920s, predated the geranium diode for a chunk of galena crystal (lead sulfide) and a piece of wire. It’s called a cat’s whisker. See photo on right. Both the diode and the crystal serve the same function. They are semi-conductors that modulate the radio waves, that the wire coil picks up, into a signal that can drive the earpiece. I don’t understand exactly how they do that. See diagram below.
So, why am I talking about radios. In the early twentieth century, radio changed American society. Before radio, people had newspapers and limited access to books. Radio brought news, information and storytelling into isolated homes in a way that changed how people spent their time and viewed the world. Radio, as a concept and physical entity, is a wonderful way to combine science with history in the classroom. Children can build and use crystal radios to learn about electricity and then explore how technology changes society. I believe STEM comes alive when children have a physical example that they made themselves.
So, back to radios. Un-powered radios can only use earpieces. Vacuum tubes could amplify 
radio signals and drive speakers so the whole family could listen. In the 1920s and 1930s, almost everyone had a radio. Even in the area where I live, that did not have electricity or telephones, farmers and ranchers bought battery powered radios. New forms of information and news from around the world poured into the remotest places.
The first transistor radio was available to the public in 1955. (Photo below) That was seventy years ago. The differences between it and a tube radio were twofold: It was more rugged, tubes were fragile, and it used less power so batteries lasted longer. Mostly, a transistor radio was small and extremely portable.
One interesting example of the influence of radio on society was presented in a recent article in American Scientist magazine (Ramirez, 2025). She discusses how the advent of the transistor radio changed the behavior of teenagers in the 1950s.
Music has always been important to people. Teenagers, a relatively new phenomenon, used popular music to define their identity. In the twenties it was jazz, in the thirties and forties it was swing, and in the fifties it was rock ‘n roll. The big tube radio had been a fixture of their parent’s living room and tied “their music” there. Teenagers always want to find freedom. The transistor radio gave them a way to take their identity along on their search. “With the transistor radio, teenagers were able to connect to one another and carve out their own culture.” (Ramiriz, 2025)
Why not try building radios in your classroom.
References
- Crystal Detector, Wikipedia.
- Crystal Radio, Wikipedia.
- Golden Age of Radio, Digital Public Library of America.
- Radio – Farm History Portal, Wessels Living History Farm.
- Transistor, Wikipedia.
- Transistor Pocket Radio, Popular Mechanics, January 1955, p. 159.
- How the Transistor Shaped Music, Ainissa Ramirez, American Scientist, September/October 2025, p. 274.
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