Advanced physics

10. (a) i. In the UK, alternating voltage in the mains is 230 V r.m.s. (2) Explain why we always use the r.m.s. value, and not the peak value to describe the mains voltage? ii. An electrical engineer needs to select a capacitor for a circuit, where it will be (3) connected to an alternating voltage source of 120 V. There are five capacitors available, with voltage ratings of: A. 100 V B. 125 V C. 150 V D. 175 V E. 200 V The higher voltage rating, the more expensive a capacitor is. Which capacitor should the engineer select? Explain your reasoning. (b) The output of an ac. voltage source is connected to an oscilloscope, the trace is shown in the diagram below. Voltage (mV) 16 12