Typically used in microwave ovens, a magnetron is a tube that utilizes electrical and magnetic currents in order to create an intense heat output. The electromagnetic energy created from a magnetron can travel at the speed of light and is the same type of energy used in radio and television broadcasting. A magnetron tube has a filament in the center which heats up when it is exposed to a slight amount of voltage or energy. The filament gives off electrons as it becomes hotter. These electrons move outward in search of positive anodes, or electrodes, but they come in contact with a magnetic field along the way.

The magnetic field within the magnetron repels the electrons. As a result, they become stuck in one area and begin rotating in circles. This creates more heat, as well as a supply of energy strong and hot enough to quickly cook an item.

In the 1920s, a General Electric employee, Albert Hull, was researching vacuum tubes when he created the magnetron. However, Hull could think of few uses for his invention, and the magnetron remained largely unused for another ten years. In the late 1930s and early 1940s, two engineers named Harry Boot and John Randall decided to explore the magnetron further. Instead of using glass to create the outer casing of the magnetron, they used heat resistant copper to create a magnetron capable of incredible microwave output. Their creation allowed for an output of 400 watts in a space smaller than four inches (10 cm).

As Boot and Randall developed stronger magnetron tubes, they discovered the tubes were ideal for sonar waves. During World War II, United States submarines began utilizing these tubes, which allowed the sonar equipment to help them detect enemy ships more quickly. In the late 1940s, Dr. Percy Spenser, who worked for Raytheon Corporation, further tested the output of magnetron tubes in his lab. He noted that the candy bar in his pocket had completely melted while working with the tubes. He decided to place a few kernels of popcorn near the machinery to see what would happen, and noticed it made the kernels pop.

Dr. Spenser called for his assistant and the two men decided to place a whole egg near the magnetron tube. When the egg exploded, Dr. Spenser realized he had discovered a fascinating form of cooking. Dr. Spenser went on to help create the world's first microwave oven in 1947. The first model weighed over 700 pounds (318 kg), was more than five feet (1.5 meters) tall, and cost more than 5,000 US dollars (USD).