911. Which of the following methods may be used to convert A.C. system to D.C ?
A. Rectifiers
B. Motor converters
C. Motor-generator sets
D. Rotary converters
E. All of the above
912. Magnetism of a magnet can be destroyed by_____________?
A. heating
B. hammering
C. by inductive action of another magnet
D. by all above methods
913. Main causes of noisy solenoid are______________?
A. strong tendency of fan out of laminations at the end caused by repulsion among magnetic lines of force
B. uneven bearing surface, caused by dirt or uneven wear between moving and stationary parts
C. both of above
D. none of the above
914. Core of an electromagnet should have____________?
A. low coercivity
B. high susceptibility
C. both of the above
D. none of the above
915. Which of the following statements is correct ?
A. The conductivity of ferrites is better than ferromagnetic materials
B. The conductivity of ferromagnetic materials is better than ferrites
C. The conductivity of ferrites is very high
D. The conductivity of ferrites is same as that of ferromagnetic materials
916. For which of the following materials the net magnetic moment should be zero ?
A. Diamagnetic materials
B. Ferrimagnetic materials
C. Antiferromagnetic materials
D. Antiferrimagnetic materials
917. Temporary magnets are used in______________?
A. loud-speakers
B. generators
C. motors
D. all of the above
918. The susceptibility of paramagnetic materials generally lies between____________?
A. KT3 and 1CT6
B. 1CT3 and 1CT7
C. KT4 and KT8
D. 10″2 and KT5
919. The attraction capacity of electromagnet will increase if the_______________?
A. core length increases i
B. core area increases
C. flux density decreases
D. flux density increases
920. For which of the following materials the saturation value is the highest ?
A. Ferromagnetic materials
B. Paramagnetic materials
C. Diamagnetic materials
D. Ferrites
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