What are the minimum requirements to cause the flow of current?
A voltage source, an ammeter, a conductor and an insulator
A voltage source, a switch and a resistor
A voltage source and a conductor
A voltage source, a conductor and an insulator
Out of the following, select the best conductor of electricity.
Graphite
China Clay
Porcelain
None of these
Which of the following statements is correct?
The resistance does not play an important role in electrical engineering.
The resistance of a wire does not depend upon its material.
The resistance of most of the materials is independent of the temperature.
The resistance of conductor is the hindrance by which the conductor opposes the flow of the current.
Resistance of a conductor increases when
its length increases
its area increases
both length and area increases
specific resistance is kept constant
The specific resistance ρ depends upon
The area of cross-section and the length of the conductor
The material of the conductor, its area of cress-section and length
The nature of the material of the conductor only
The area of cross-section of the conductor
The specific resistance ρ is defined as
resistance of a conductor which has a length of 1 m and cross-section of 1 m2 at 20C
resistance of any conductor at 25C
resistance of any conductor at 20C
resistance of a conductor which has a length of 1 m and cross-section of 1 cm2 at 20C
The resistance of a conductor, when its temperature is increased
remains constant
increases
varies
decreases
It was experimentally found by James Prescott Joule that the heat produced in a current carrying conductor is proportional to
the square of the current
square of resistance
the current
inversely proportional to time
The value of Joule's mechanical equivalent of heat, J, is equal to
4.2 calories per Joule
2.4 Joules per calorie
4.2 Joules per calorie
4.2 Joules
Temperature coefficient of a conductor is defined as the
increase in resistance per ohm per degree centigrade
increase in resistance per degree centigrade
increase in resistance per degree absolute
decrease in resistance per ohm per degree centigrade
When current flows in a conductor, heat is produced because
heat α I²
of electronic collision
of interatomic collision
of Joule's law
Heating effect of current has undesirable side effect in
electric oven
electric iron
immersion heater
vacuum cleaner
The resistance of carbon (filament in carbon-filament lamps) when its temperature is decreased
remains the same
increases enormously
The curve representing Ohm's law is
a parabola
linear
sine function
a hyperbola
The condition in Ohm's law is that
ratio V/I should be constant
current should be proportional to voltage
the temperature should remain constant
the temperature should vary
Ohm's law does not apply to
conductors
conductors when there is change in temperature
semiconductor
a.c. circuit
Ohm's law is applicable to
electric arc
rectifying devices
gas discharge lamps
none of these
Ohm's law can be applied with certain reservations to
semiconductors
electrolytes
thermionic valves
The presence of an electric current is made known by
flashing
effects produced
cracking
electric shock
An electric current can neither be ____ nor ____.
felt, seen
seen, touched
seen, produced by any effect
produced, felt
The presence of the current is only made known by the effect it produces. Three important effects are
heating, electric shock and generation
generation, chemical and electric shock
heating, magnetic and electric shock
heating, magnetic and chemical
Voltage applied across a circuit, acts as
mass of electrons
negative ions
a component of current
a force
In a series circuit the current is
constant
always zero
proportional to the resistance
different from resistors
In a parallel circuit the potential difference across the resistance
is different from the applied voltage
is sometimes constant
is always constant
The resistance R1 and R2 are connected in parallel. The ratio of values of resistance R1 : R2 is 4 : 1. The currents in R1 : R2 will be equal to
1 : 4
1 : 1
4 : 1
4 : 4
A resistance of 4 ohms is connected across 100 V supply. When another resistor 'R' ohms is connected in parallel with 4 ohms, the total current taken from supply was found to be 50 A. The value of resistance 'R' is
2 ohms
3 ohms
5 ohms
4 ohms
The voltage applied across an electric press was reduced by 50%. The power consumed by the press will be reduced by
25%
75%
60%
50%
Two electric presses are connected in parallel. The resistance of the first press is 100 ohms and that of the second is 300 ohms. The total current taken by both the presses is 4 A. The ratio of current taken by first : second will be equal to
2 : 3
1 : 3
3 : 1
1.2 : 3
Three elements having conductance G1. G2 and G3 are connected in parallel. Their combined conductance will be
G1 + G2 + G3
1/(G1 + G2 + G3)
(G1G2 + G2G3 + G3G1)/(G1 + G2 + G3)
1/(1/G1 + 1/G2 + 1/G3)
Four resistance R1, R2, R3 and R4 are connected in series against 220 V supply. The resistances are such that R1 > R2 > R3 > R4. The least power consumption will be in
resistor R1
resistor R4
resistor R3
resistor R2
When current flows through heater coil it glows but supply wiring does not glow because
supply wiring is covered with insulation layer
current through supply line flows at slower speed
supply wires are made of superior material
resistance of heater coil is more than that of supply wires
Resistors commonly used in power circuits are
carbon resistors
etched circuit resistors
wire wound resistors
deposited metal resistors
International ohm is defined in terms of resistance of
a column of mercury
a cube of carbon
unit length of metal wire
a cube of copper
Which of the following has negative coefficient of resistance?
wire wound resistor
non-metals
thermistor
metals
The current carrying capability of the fuse material depends on
length
material
cross-sectional area
all of these
