Vacuum tube era: In which decade were the first successful <diode> and <triode> vacuum tubes invented? Recall that the diode (Fleming) and triode (de Forest) appeared just a few years apart in the early 20th century. Choose the correct decade.

Given data

• The first successful diode vacuum tube (Fleming) and triode (de Forest) are being dated by decade.

Concept / Approach
Fleming's diode was demonstrated in 1904; Lee de Forest's triode (Audion) followed in 1906. Both events lie within the same decade.

Step-by-step calculation
Years 1904 and 1906 → fall in the 1900–1909 interval ⇒ decade = 1900s.

Common pitfalls

• Confusing the triode's widespread commercialization (later) with the decade of first invention.

Final Answer
1900s.