Exam-style question
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Which of the following best describes the output waveform of a 555 timer in astable mode?.
- A.A pulse train with variable duty cycle
- B.A sine wave
- C.A square wave
- D.A triangular wave
Model answer
What a good answer should say
- A pulse train with variable duty cycle
Explanation
Why this works
Rule: In astable mode the 555 timer continuously oscillates, producing a square‑wave output whose high time is set by R1+R2 and low time by R2. The duty cycle can be adjusted by changing the resistors, so the waveform is a pulse train with variable duty cycle.
Common mistake
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