(b) A 480 V, 220 kVA, 0.80 power factor lagging, 40 Hz, two-pole, Y-connected synchronous generator has a synchronous reactance of 1.2 2 and an armature resistance of 0.035 2. Its friction and windage losses are 22 kW, and its core losses are 10 kW. The field circuit has a DC voltage and maximum Ip of 200 V and 9 A, respectively. The resistance of the field circuit is adjustable from 20 2 to 200 2. The Open Circuit Characteristic (OCC) of this generator is shown in Figure Q1(b). (i) Explain the field current when the generator is running at no load using OCC in Figure Q1(b). (ii) By referring to Figure Q1(b) the field current of the generator is adjusted to 3A. Determine the terminal voltage of this generator if it is connected to a A connected load with an impedance of 20430° 2. (iii) Calculate the efficiency of the generator. (iv) Formulate the speed in rpm and torque applied to the generator. 600 540 > 480 420 360 300 240 180 120 60 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 Field current, A Open circuit terminal voltage, V

(b) The circuit in Figure Q2 (b) below shows a rectifier circuit where Vin is a 10kHz sine wave with an amplitude of 2Vpp and RL is 10k. (i) (iii) The componet between A and B is a PN diode, sketch and label its silicon structure and explain its characteristics. Sketch the waveforms you would see at A and B and explain or sketch how you would connect your scope probes to measure them. Label your sketches clearly showing values and axis details. Comment on any similarities or differences between the waveforms at A and B.

Worked Example 1-1 Express the following numbers in scientific notation: a) 408.00 b) 0.007956

Dopant density (cm-³) 1021 1020 1019 1018 1017 1016 10¹5 1014 1013 10¹2, 10-4 10-3 10-¹ 10⁰ 10¹ 10² 10³ 104 Resistivity (ohm-cm) FIGURE 2-8 Conversion between resistivity and dopant density of silicon at room temperature. (After [3].) N type 10-2 P type EXAMPLE 2-3 Temperature Dependence of Resistance a. What is the resistivity, p, of silicon doped with 10¹7cm-3 of arsenic? b. What is the resistance, R, of a piece of this silicon material 1 um long and 0.1 μm² in cross-sectional area? c. By what factor will R increase (or decrease) from T = 300 K to T = 400 K? d. What As concentration should one choose if she wishes to minimize the change in (c)?