(D) Any 3 of these: Chemical reactions, as in a battery, Electromagnetic generators, Photovoltaic cells (solar), Generators that convert mechanical energy to electrical energy, Friction, Thermoelectrical sources
9 >>Beyond the atomic structure of a material, name two things that affect the conductivity of a material. ?
(A) 3.08 mA from D to B
(B) 2.17 per cent high
(C) negatively 3. ion
(D) The physical characteristics and the temperature
(D) The physical characteristics and the temperature
11 >>Describe, with the aid of a circuit diagram, how a simple potentiometer can be used to check the calibration of a d.c. ammeter.The current through an ammeter connected in series with a standard resistor of 0.1 ? was adjusted to ?
(A) 3.08 mA from D to B
(B) 2.17 per cent high
(C) negatively 3. ion
(D) The physical characteristics and the temperature
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12 >>The arms of a Wheatstone bridge have the following resistances: AB, 10 Ω; BC, 20 Ω; CD, 30 Ω; and DA, 10 Ω. A 40 Ω galvanometer is connected between B and D and a 2 V cell, of negligible internal resistance, is connected across A and C, its positive end being connected to A. Calculate the current through the galvanometer and state its direction. ?
(A) 3.08 mA from D to B
(B) 2.17 per cent high
(C) negatively 3. ion
(D) The physical characteristics and the temperature
13 >>Describe with the aid of a circuit diagram the principle of the Wheatstone bridge, and hence deduce the balance condition giving the unknown in terms of known values of resistance. In a Wheatstone bridge ABCD, a galvanometer is connected between B and D, and a battery of e.m.f. 10 V and internal resistance 2 ? is connected between A and C. A resistor of unknown value is connected between A and B. When the bridge is balanced, the resistance between B and C is 100 ?, that between C and D is 10 ? and that between D and A is 500 ?.Calculate the value of the unknown resistance and the total current supplied by the battery. ?
(A) 33.8 kΩ
(B) 60.67 Ω; 9.9 per cent high
(C) 776 Ω
(D) 5000 Ω; 21.45 mA
14 >>A permanent-magnet moving-coil milliammeter, having a resistance of 15 Ω and giving full-scale deflection with 5 mA, is to be used with bridge-connected rectifiers (Fig. 43.16), and a series resistor to measure sinusoidal alternating voltages. Assuming the ‘forward’ resistance of the rectifier units to be negligible and the ‘reverse’ resistance to be infinite, calculate the resistance of the series resistor if the instrument is to give full-scale deflection with 10 V (r.m.s.). ?
(A) 30.4 μN m
(B) 51.2 mA
(C) 0.9; 1.036
(D) 1786 Ω
15 >>Explain with the aid of a circuit diagram showing the connections made to the cathode-ray oscilloscope, how it may be used to determine the r.m.s. value of an a.c. signal which is: (a) sinusoidal; (b) non-sinusoidal.An oscilloscope is used to display a sinusoidal alternating voltage. The display shows a sine wave of amplitude 3.3 cm and the Y-amplifier sensitivity is set to 5 V/cm. Determine the r.m.s. value of the voltage. ?
(A) 9.8 V per volt
(B) 1600 r/min
(C) 96.94 V
(D) 23.3 V
16 >>For the system in Q. 5, the load speed is adjusted to 1900 r/min. Determine the corresponding reference voltage. ?
(A) 9.8 V per volt
(B) 1600 r/min
(C) 96.94 V
(D) 23.3 V
17 >>For the system in Q. 5, the reference voltage is reduced to 80 V. Determine the corresponding reference speed. ?
18 >>For the speed control system shown in Fig. 44.10, the tachogenerator (feedback transducer) has a transfer function of 50 mV per r/min and the transfer function for the motor/load is 100 r/min per volt. The reference signal applied to the system is 100 V. Given that the allowable speed error is 40 r/min, determine the amplifier gain (transfer function). ?
(A) 9.8 V per volt
(B) 1600 r/min
(C) 96.94 V
(D) 23.3 V
19 >>The rectifier network in Q. 4 is replaced by a threephase bridge rectifier. Again determine: (a) the mean load current; (b) the mean load voltage. ?
(A) 122.5°
(B) 2.06 A, 136.2°
(C) 5.61 A, 280.7 V
(D) 6.48 A, 323.9 V
20 >>Describe the various losses which take place in a shunt motor when it is running on no load. A 230 V shunt motor, running on no load and at normal speed, takes an armature current of 2.5 A from 230 V mains. The field-circuit resistance is 230 ? and the armature-circuit resistance is 0.3 ?. Calculate the motor output, in kW, and the efficiency when the total current taken from the mains is 35 A. If the motor is used as a 230 V shunt generator, find the efficiency and input power for an output current of 35 A. ?
