In what year was the cavity magnetron developed?

• A. 1925
• B. 1939
• C. 1950
• D. 1964

Answer: (B)

The key idea here is when the cavity magnetron first became a practical microwave oscillator that powered early radar work. In the late 1930s, researchers at Birmingham, led by Randall and Boot, built and demonstrated the first working cavity magnetron. The pivotal demonstrations and results were achieved by 1939, making it the year associated with its development. This breakthrough drastically increased microwave power and efficiency, enabling more capable radar systems during that era. The other years are well before or after the actual breakthrough, so they don’t fit the timeline of when the cavity magnetron was developed.