Ques 71. A current of 2A passes through a coil of 350 km would on a ring with a mean diameter of 12 cm. The flux density established in the ring is 1.4wb/m2. Find the value of relative permeability of Iron
191
1200
600✔
210 × 103
Given
i = 2A
B = 1.4 wb/m2
N = 350
D = 12cm = 0.12 m
The magnetomotive force in ampere-turns can be expressed as:
F = NI
= 350 × 2 = 700 AT
Ques 72. Electrical resistivity ρ is:
High for copper as well as for alloy
Low for copper and high for alloy✔
High for copper and low for alloy
Low for copper as well as for alloy
Electrical resistivity, represented by ρ (rho), is a measure of how strongly a material opposes the flow of electric current. The lower the resistivity, the more readily the material permits the flow of electric charge.
The electrical resistivity of the copper is low as its conductivity is high whereas the electrical resistivity of the alloy is more
Ques 73. Silicon has a preference for IC technology because?
It is an indirect semiconductor
It is an elemental semiconductor
It is a covalent semiconductor
Of the availability of nature oxide SiO2✔
SiO2 plays an important role in IC technology because It acts as a diffusion mask permitting selective diffusions into silicon wafers through the window etched into oxide and no other semiconductor material has a native oxide that is able to achieve all the properties of SiO2.
It acts as the active gate electrode in the MOS device structure.
It provides electrical isolation of multilevel metallization used in VLSI.
SiO2 is used to isolate one device from another.
Ques74. In dc operation of a fluorescent tube, the life of the tube
Remain same
Decrease by about 80% as that with AC operation✔
May increase or decrease
Increase by about 80% as that with AC operation
By using the fluorescent tube in DC operation the tube life is decreased by 80% due to the presence of ripple.
Ques 75. If the number of turns of a coil is increased, its inductance
Remain the same
Decreased
Increased✔
None of the above
With an increase in the number of coils, the flux linkage in the coil is increased which increases the overall inductance of that coil.
Ques 76. Which instrument is used to measure the high resistance?
Ques 77. A resistor is connected across a 50 V source. The current in the resistor if the color code is red, orange, orange, or silver is?
21.4 mA
2 mA
2.2 mA✔
214 mA
Resistor values can be known by the color band.
0 black
1 blue
2 red
3 orange
4 yellow
5 green
6 blue
7 violet
8 grey
9 white
First color = digit
Second color=digit
Third color= power of ten
Fourth color =tolerance
In a resistor, the first color means the value first digit that is
Red – 2
Orange – 3
but that next on Orange means the power of 10
Orange – 103
that color code silver means to withstand the power of the resistor +/- 10%.
We get the Resistance value from the color code (red, orange, orange, silver) is 23 (103) = 23000.
Here we are not considering the last color (tolerance-silver) Because in the question there is no specification of minimum or maximum current.
So current I = V/R = 50/23000 = 0.00217 = 2.2mA.
Ques 78. Which of the following motor is used in the mixer?
Reluctance motor
Universal Motor✔
Repulsion Motor
Hysteresis Motor
We use universal motors in mixer grinders. Universal motors can run both on a.c. and d.c.These motors have high starting torque and speed, hence these are most preferred.
Ques 79. The Ta vs Ia is a graph of a DC series motor is a
Straight-line throughout
Parabola from no load to overload
Parabola throughout
Parabola up to full load and straight line after saturation✔
Ta vs Ia graph of DC series motor
In the case of the DC series, motor torque is proportional to the square of the armature current and this relation is parabolic in nature.
Ta vs Ia graph of DC series motor
As load increases, armature current increases and torque produced increases proportional to the square of the armature current upto a certain limit.
After reaching the Saturation point though the current through the winding increases, the flux produced remains constant. Hence after saturation, the Ta Ia takes the shape of a straight line as flux becomes constant.
Ques 80. The no-load primary current Io is about ________ of full load primary current of a transformer.
3-5%✔
above 40%
15-30%
30-40%
A transformer is said to be on “no-load” when its secondary side winding is open-circuited. When the transformer is in no-load condition there will be no current in the secondary section. The losses on the primary side are the core loss, dielectric loss and copper loss due to excitation current are the no-load losses and usually, they are pretty small which is about 2 – 5% of full load.
