(b) A spherical electrode has to be fitted to a 20 mm diameter rod as shown in Fig. 2.17 (top). Determine the diameter of the sphere if the electrodes are at 100 kV rms. Assume the distance to the laboratory phorel walls to be 5 m. (Hint: regard the laboratory as an outer cylinder with a 5 m radius and ensure that the maximum stresses on the cylindrical and spherical sections are equal.) (R1= 62.15 mm) (5) (c) In Fig. 2.17, r, = 30 mm. Determine the other dimensions by ensuring that the maximum field Fig. 2.17: Question 3 strengths in the cylindrical and spherical sections are equal. Determine the maximum working voltage of the system if the stress has to remain below 2 KV/mm. (Hint: Use the optimal r2/r, - and R2/R,-ratios). (r2=81.54 mm, R,= 60 mm, R2= 120 mm, V= 60 kV)