225.  A sinusoidal e.m.f.
A. leads the flux inducing it by 1800
B. leads the flux inducing it by 90?
C. lags the flux inducing it by 180?
D. lags the flux inducing it by 90?

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226. The humming sound in a transformer is mainly due to
A. magnetostriction
B. walls of the tank
C. oil of the transformer
D. laminations of the transformer

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227.  The advantage of putting tappings at the phase ends of a transformer is
A. to reduce the number of bushings
B. to obtain better regulation
C. to obtain fine variation of voltage
D. to operate with ease

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228. In a three-phase delta transformer, one of the phases burns up. The transformer will supply
A. zero output
B. 20 percent of its output rating
C. 40 percent of its output rating
D. none of the above

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229. When a 440/220 V transformer is connected to 400 V D.C. supply
A. the transformer may burn
B. the outupt will be zero volt
C. the output will be 220 V
D. the output will be less than 230 V

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230. In high frequency transformer ferrite cores are used because a ferrite core has
A. low resistance
B. high resistance
C. low permeability
D. high hysteresis

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231. Which of the following transformers is smallest?
A. 2 kVA, 500 Hz
B. 2 kVA, 400 Hz
C. 2 kVA, 200 Hz
D. 2 kVA, 50 Hz

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