Question-1: The induced magnetic force, given by Find = i (L x B), is called motor action and the induced magnetic force, given by eind = (V × B).L, is called generator action. a) Explain the role of induced forces in generators when we expect generators to be all about induced voltages and not induced forces? b) Explain the role of induced voltages in motors when we expect motors to be all about induced forces and not induced voltages?

This question is about d.c. machinesa)Explain briefly why the terminal voltage of a d.c. machine is not equal to thegenerated or back emf except at no load when V = E.b)Hence, state the relationship between V, E, the armature current and resistance thatapplies at normal loads for a generator.c)A 250 V shunt motor has an armature resistance of 0.4 Ω and runs at a speed of 750 rev min –1 when taking a full load current of 25 A.i)Estimate the speed of the motor at no load when the armature current is 3 A, assuming that the flux per pole remains constant.ii)Derive the relationship between speed, emf, and flux.iii)Calculate the field current for a field resistance of 110 Ω, if the load torque remains constant;iv)calculate the new armature current if the speed is increased to 1000 rev min –1v)Hence, find the value of the additional resistance required in the field circuit to maintain this current d)If the field current of a shunt wound d.c. motor is halved, what effect will thishave on the…

× 4:03 K s.eng.ruh.ac.lk □ Û 8. Figure 4 shows the core of a simple dc motor. The magnetization curve for the metal in this core is given by Figure 5 and Figure 6. Assume that the cross-sectional area of each air gap is 18 cm² and that the width of each air gap is 0.05 cm. The effective diameter of the rotor core is 4 cm. L It is desired to build a machine with as great a flux density as possible while avoiding excessive saturation in the core. What would be a reasonable maximum flux density for this core? ii. What would be the total flux in the core at the flux density of part (i)? iii. The maximum possible field current for this machine is I A. Select a reasonable number of turns of wire to provide the desired flux density while not exceeding the maximum available current. Flux Density, B (T) 2.8 སྤྲ ཤཱ ཀ ཀཱ བྷ ཀ ཡཱཾ བ ་ 1.2 1.0 0.4 0.2 4-48cm Figure 4 0 10 20 30 40 50 100 → Depth 4 cm -0.05 cm 200 300 500 1000 2000 Magnetizing Intensity, H (A.turns/m) Figure 5 Magnetization curve…