Final answer:
The DC average of a square wave with a voltage varying between 0 V and 12 V, with 25ms positive pulses and a 75ms gap between them, is 3 V. This is calculated by finding the duty cycle, 25%, and then multiplying the peak voltage by the duty cycle.
Step-by-step explanation:
To calculate the DC average of the waveform, you need to account for the time the voltage is at its high level and the time it is at zero volts. The square wave voltage varies between 0 V and 12 V. We can use the duty cycle of the waveform to determine the average voltage. A duty cycle is the percentage of one period in which a signal is active. In this case, the active time (pulse width) is 25ms and the total period of the waveform (pulse width plus gap) is 25ms + 75ms = 100ms.
The duty cycle can be calculated as follows: (Pulse Width / Total Period) * 100 = (25ms / 100ms) * 100 = 25%. Now, to find the average voltage, we multiply the peak voltage (12 V) by the duty cycle (as a decimal). Thus, the DC average voltage is 12 V * 0.25 = 3 V. Hence, the DC equivalent for this square wave is 3 volts.