Due to which of the following reasons aluminium does not corrode in atmosphere ?
Atmospheric oxygen can only diffuse very slowly through the oxide layer which is formed on the surface of aluminium
none of the above
No reaction with oxygen occurs ft Any of the above
Aluminium is a noble metal
Atmospheric oxygen can only diffuse very slowly through the oxide layer which is formed on the surface of aluminium
Due to which of the following fact in India aluminium is replacing copper ?
Aluminium is available in plenty cheaper and lighter than copper
Aluminium has lower resistivity than that of copper
Aluminium is more ductile and malleable than copper
Aluminium has less temperature co-efficient than copper
Aluminium is available in plenty cheaper and lighter than copper
The conduction of electricity in semiconductors takes place due to movement of
positive and negative ions
electrons and holes
positive ions only
negative ions only
electrons and holes
________ has the best damping properties.
Cast iron
Diamond
High speed steel
Mild steel
Cast iron
The photo-electric effect occurs only when the incident light has more than a certain critical
wave length
speed
intensity
frequency
frequency
If the resistance of a conductor does not vary in accordance with Ohm’s law it is known as
reverse conductor
bad-conductor
non-linear conductor
non-conductor
non-linear conductor
Effect of moisture on the insulating materials is to
all of the above
increase dielectric loss
decrease dielectric strength
decrease dielectric constant
all of the above
A good electric contact material should have all of the following properties except
high resistivity
good thermal conductivity
high resistance to corrosion
high melting point
high resistivity
Most of the common metals have _____ structure.
orthorhombic
cubic
linear
hexagonal
cubic
Non-linear resistors
produce harmonic distortion
follows Ohm’s law at low temperatures only
result in non-uniform heating
none of the above
produce harmonic distortion
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