1.A 200 ohms metallic strain gauge with gauge factor 2.0 when subjected to a strain of 500 micro-strain will have a total change in resistance of
Answer : 2 ohm
Explain:-
2.A Capacitive circuit of 50 microF and of negligible resistance is connected across a 300V, 50 Hz 1-phase supply. The rms value of current drawn by the circuit is
Answer : 4.72 A
Explanation:-
Given a Capacitive circuit of C=50microF and R=0ohm
Voltage=300v, f=50Hz
Impedance of circuit = Capacitive Reactance(Xc) (R=0)
Z=1/(2Ï€*50*50*10^-6)=63.66 Ohms
Current=Voltage/Impedance=300/63.66=4.72 A
3.An alternating current of frequency 50 Hz and maximum value 200A is given as
Answer : i= 200 sin 314t
Explanation:-
Given Maximum value of current(Imax)=200A and frequency=50Hz
Current(i)=Imax*sinωt
ω=2πf=2*3.14*50=314
i=200 sin 314t
4. A series resonant circuit has
Answer : Unity p.f. and minimum current
Explain:-
5. Three equal impedances are first connected in delta across a three phase balanced supply. If the same impedances are connected in star across the same supply, then
Answer : Line current will be one third
Explain:-
6.W1 and W2 are the readings of two wattmeters used to measure power of a 3 phase balanced load. The reactive power drawn by the load is
Answer : √3 (W1-W2)
Explain:-
7.In an ideal transformer which of the following is true
Answer : Copper and core losses are zero
Explain:-
8. The ratio of core loss to copper loss at full load is 0.5, the maximum efficiency occurs when the load is
Answer : 0.7071 of full load
Explain:-
9. Mineral oil is used in transformer as
Answer : Cooling and insulating medium
Explain:-
10.The p.u. equivalent resistance and reactance frops of a transformer are 2.0 and 4.0 respectively. If the transformer operates at 0.6 lagging p.f., the percentage of voltage regulation is
Answer : 4.4
Explain:-
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