Schmitt Trigger Astable Multivibrator If the timing resistor is variable, which characteristic of the output waveform changes when the resistance is adjusted?

Introduction / Context:
In RC oscillators and 555 astable circuits (including Schmitt trigger based astables), the timing resistor and capacitor set the charge and discharge time between thresholds. This determines frequency and duty cycle.

Given Data / Assumptions:

• Variable resistor forms part of the RC timing path.
• Schmitt thresholds remain fixed by design or by the internal divider.
• Supply voltage is constant within normal limits.

Concept / Approach:
Changing R alters the time constant tau = R * C. Since the period depends on how long it takes the capacitor to move between threshold voltages, increasing or decreasing R changes period and frequency. Waveform amplitude is usually near logic rails and does not change due to R alone.

Step-by-Step Solution:
1) Time constant: tau = R * C.2) For 555 astable, period T is proportional to (RA + 2 * RB) * C. Varying the timing resistor changes T.3) Amplitude is set by supply rails and device output stage, not R in the timing leg.4) Shape remains a rectangular wave with similar transitions; duty cycle may shift but the fundamental shape does not.

Verification / Alternative check:
Oscillator equations show linear dependence of period on R for a fixed C and thresholds.

Why Other Options Are Wrong:

• the shape of the waveform: Still a rectangular wave; only frequency and duty cycle vary.
• the amplitude of the waveform: Dominated by supply and output stage; R does not set amplitude.
• none of the above: Incorrect because period clearly changes with R.

Common Pitfalls:
Confusing duty cycle change with amplitude or shape changes; assuming larger R reduces amplitude, which is not the case for digital level outputs.

Final Answer:
the period of the waveform