Which of the following is an advantage of stranded conductor over equivalent single conductor ?
Less liability to break
All of the above
Less liability to kink
Greater flexibility
All of the above
Due to which of the following reasons copper and aluminium are not used for heating elements ?
All of the above
Both have great tendency for oxidation
Both have low melting point
Very large length of wires will be required
All of the above
Copper even though costly finds use in the windings of electrical machines because
copper windings are less bulky and the machines become compact
copper can be easily soldered and welded
copper points offer low contact resistance
all of the above
all of the above
Substances whose specific resistance abruptly decreases at very low temperature are called
insulators
conductors
superconductors
semiconductors
superconductors
Which of the following affect greatly the resistivity of electrical conductors ?
Composition
Temperature
Size
Pressure
Composition
Thermonic emission occurs in
vacuum tubes
ferrite cores
copper conductors
transistors
vacuum tubes
Which of the following materials does not have covalent bonds ?
transistors
Metals
Organic polymers
Silicon
Metals
The conductivity of a metal is determined by
the electronic concentration and the mobility of the free electrons
the number of valence electrons per atom
either or
none of the above
the electronic concentration and the mobility of the free electrons
The resistivity of a metal is a function of temperature because
none of the above
the electron gas density varies with temperature
the electron density varies with temperature
the amplitude of vibration of the atoms varies with temperature
the amplitude of vibration of the atoms varies with temperature
In a crystal an atom vibrates at a frequency determined by
the heat content of the crystal
the temperature of the crystal
the stiffness of the bonds it makes with neighbors
none of the above
the stiffness of the bonds it makes with neighbors
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