129/22

86. Which of the following is true ?
i. Oscilloscope is basically a voltmeter
ii. CRO is a fast x-y plotter
iii. Effect of negative voltage to the grid is an attractive force
iv. Focusing and accelerating anodes are cylindrical
v. During flyback period, voltage is very high
A) All are true
B) Only i, ii and iv are true
C) Only i and ii are true
D) Only i and iv are true

87. The inductance of a moving iron instrument is given by :
L = (40 + 20 - 0ಶ1, where 0 is the deflection in radians from zero position. The
spring constant is 12 x 10-6 Nm/rad. Estimate the deflection for a current of 2A.
A) 0.5 rad B) 0.25 rad
C) 0.15 rad D) 0.75 rad

88. A simple equal arm voltage sensitive bridge is initially balanced. Three of the arms
consists of ordinary resistors, while the fourth is a thermistor. Each arm has a
nominal resistance of 1KQ and the bridge is energised with a 10V dc source. If a
temperature change causes a + 15% change in thermistor resistance, what output
voltage (approximately) will be indicated from the bridge ?

A) 349 mV B) 35 mV
00 ۷ D) None of these

89. Which of the following is true ?
i. An ammeter is used for measuring magnitude and direction of current flow
ii. D’ Arsonval galvanometer is used to measure small voltage and current in the
circuit
iii. Galvanometer connected with high resistance in series is used as ammeter
iv. A galvanometer also is known as PMMC instrument
A) Only i, ii and iv are true
B) Only i and iv are true
C) Only ii, iii and iv are true
D) Only ii and iv are true
90. The two-wattmeter method is used to measure power in a balanced 3-phase circuit,

drawing lagging current. The power factor if one of the wattmeters reads twice the
value of the other wattmeter.

^) 1/\2 B) 1 C) 1/2 0) 13/2
A -13-