Timing Circuit - Buzzer

Masafi

In a timing circuit, an electronic processor operates so that the buzzer sounds when Vc is greater than Vs.

The switch S is normally open. Explain in detail what happens in the circuit after the switch S is closed for a moment then opened again. Your answer should include an appropriate calculation and a sketch graph.

Answer is:

S closed --> C charges
up to Vs
Instantly/very quickly
S open: discharge starts
Exponential discharge
Vc = Vs e^(-t/RC)
¾ Vs = Vs e^(-t/RC)
ln ¾ = -t/RC (1)
t = 29.7 s

Buzzer sounds for 29.7 s

However, shouldnt the answer be 2 x 29.7, as the buzzer also sounds during the time the capacitor is charged and Vc > 0.75Vs?