NOTE: Thanks to Yaodong Tang who pointed out that the increase in capacitance will only compensate and may make the AVERAGE Voltage of output 12V. However, to fully regulate this voltage the MINIMUM Voltage coming to be regulated by Zener has to be 12V. In the previous case where capacitor is changed, it will never make the minimum voltage across Zener 12V. So the two changes should be, put a voltage regulator of 12V in parallel with the capacitor. 2. Increase the AC input voltage so that the minimum voltage to be regulated is 12V.
NOTE: The correct solution to Q1 Detailed study 1 is ‘Earth, interference, no’.
NOTE: For Electronics/photonics Q2, the correct period is 1 ms.