Resistance of a material always decreases if
none of the above is correct
temperature of material is increased
temperature of material is decreased
number of free electrons available become more
number of free electrons available become more
If the efficiency of a machine is to be high what should be low ?
Input power
True component of power
Losses
kWh consumed
Losses
When electric current passes through a metallic conductor its temperature rises. This is due to
collisions between conduction electrons and atoms
mutual collisions between conducting electrons
mutual collisions between metal atoms
the release of conduction electrons from parent atoms
collisions between conduction electrons and atoms
The resistance of a conductor varies inversely as
area of cross-section
temperature
length
resistivity
area of cross-section
With rise in temperature the resistance of pure metals
remains constant
increases
decreases
first increases and then decreases
increases
With rise in temperature the resistance of semi-conductors
decreases
increases
first increases and then decreases
remains constant
decreases
Two resistors are said to be connected in series when
sum of IR drops equals the applied e.m.f.
total current equals the sum of branch currents
both carry the same value of current
same current passes in turn through both
same current passes in turn through both
Which of the following statement is true both for a series and a parallel D.C. circuit?
Elements have individual currents
Currents are additive
Power are additive
Voltages are additive
Power are additive
Which of the following materials has a negative temperature co-efficient of resistance?
Carbon
Brass
Aluminum
Copper
Carbon
Ohm’s law is not applicable to
vacuum tubes
high voltage circuits
carbon resistors
circuits with low current densities
vacuum tubes
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