A. Speed of the machine
B. Contact pressure
C. Surface conditions of brush and commutator
D. Excessive sparking
E. All of the above
Related Mcqs:
- On which of the following factors does the resistivity of a material depend ?
A. Resistance of the conductor
B. Area of the conductor section
C. Length of the conductor
D. All of the above - Which of the following factors affect resistivity of metals ?
A. Age hardening
B. Alloying
C. Temperature
D. Cold work
E. All of the above - Due to which of the following reasons aluminium does not corrode in atmosphere ?
A. Aluminium is a noble metal
B. Atmospheric oxygen can only diffuse very slowly through the oxide layer which is formed on the surface of aluminium
C. No reaction with oxygen occurs ft Any of the above - Due to which of the following reasons copper and aluminium are not used for heating elements ?
A. Both have great tendency for oxidation
B. Both have low melting point
C. Very large length of wires will be required
D. All of the above - Due to which of the following fact, in India, aluminium is replacing copper ?
A. Aluminium is more ductile and malleable than copper
B. Aluminium is available in plenty, cheaper and lighter than copper
C. Aluminium has lower resistivity than that of copper
D. Aluminium has less temperature co-efficient than copper - The conductors have transport phenomena of electrons due to____________?
A. electric field
B. magnetic field
C. electromagnetic field
D. none of the above - The conduction of electricity, in semiconductors, takes place due to movement of______________?
A. positive ions only
B. negative ions only
C. positive and negative ions
D. electrons and holes - In conductors conduction of electricity takes place due to movement of_______________?
A. electrons only
B. positive ions only
C. negative ions only
D. positive and negative ions
E. none of the above - Surface resistance of an insulating material is reduced due to the______________?
A. smoky and dirty atmosphere
B. humidity in the atmosphere
C. both (A) and (b)
D. neither (A) nor (b) - The current due to electron flow in conduction band is the hole current in valence band?
A. equal to
B. less than
C. greater than
D. any of the above
