A domestic mixer uses the __________ motor

A domestic mixer uses the __________ motor

(A) induction motor
(B) reluctance motor
(C) universal motor
(D) permanent magnet synchronous motor

Answer : universal motor

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If the no of valence electrons in an atom is less than four, then it is referred as .......................

If the no of valence electrons in an atom is less than four, then it is referred as .......................

a. semiconductor

b. conductor

c. insulator

Answer:

valence electron <  4 - conductor

valence electron > 4 - insulator

valence electron  = 4 - semiconductor 

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Which of the following equations is valid for a 3-phase 4-wire balanced star-connected load?

Which of the following equations is valid for a 3-phase 4-wire balanced star-connected load?

(a) IR + IY + IR = IN = O
(b) IN + IY – IB = IN
(c) IR – IY + IB = IN
(d) VB + VR + VY ⁄ Z =N


Answer: IR + IY + IR = IN = O

Balanced  circuit means the magnitude of each phase current is equal and neutral current is zero.

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The number of protons in silicon and germanium atom is

The number of protons in silicon and germanium atom is

a) 4 ,32
b) 16,32
c) 28,14
d) 14,32

Answer : 14,32

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According to KVL, the algebriac sum of all IR drops and emf is in any closed loop of a network is always

According to KVL, the algebriac sum of all IR drops and emf is in any closed loop of a network is always

a. zero
b. postive
c. negative
d. determined by battery emfs.

Answer: The algebraic sum of voltage drops and emfs in a closed circuit is equal to zero.

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The period of a sine wave is 1/50 seconds. its frequency is

The period of a sine wave is 1/50 seconds. its frequency is

A. 20 HZ
B. 30 HZ
C. 40 HZ
D. 50 HZ

Answer: 50 HZ

F = 1/T  = 50 HZ

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A DC chopper remains ON for 36 μs. and OFF for 12 μs.What is its duty cycle ?

A DC chopper remains ON for 36 μs. and OFF for 12 μs.What is its duty cycle ?

A. 0.25

B. 0.75

C. 0.5

Answer: 0.75



Ton  = 36 μs.

Toff = 12 μs.

T = Ton + Toff = 48 μs.

Duty cycle = Ton / T

                  = 36 / 48
              
                  = 0.75

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The electric motor used in portable drills is.............

The electric motor used in portable drills is.............

a.capacitor-run motor
b.hysteresis motor
c. universal motor
d. repulsion motor

Answer: universal motor

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The quantity of charge that will be transferred by a current flow of 10 A over 1 hour period is

The quantity of charge that will be transferred by a current flow of 10 A over 1 hour period is

a. 10 C
b. 36000 C
c. 2400 C
d. 160 C

Answer:

t= 1 hr = 3600 sec

Q=I*t  = 10*1*3600 = 36000 coulombs

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Permanent magnet moving coil instrument can be used for ..........

Permanent magnet moving coil instrument can be used for ..........

a. ac work only
b. dc work only
c. both dc and ac work
d. none of the above.

Answer: dc work only

In a.c, the deflecting torque of the instrument reverses if the current reverses and hence the pointer cannot follow the rapid  reversals and the deflection corresponds to  a mean torque value of zero.so these instruments cannot be used for a.c.

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In a.c system, we generate sine waveform because....................

In a.c system, we generate sine waveform because....................

a. it can be  easily drawn.
b. it produces least distrubance in electrical circuits.
c.it is nature standard.
d.other waves cannot be produced easily.

Answer:it produces least distrubance in electrical circuits.

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What is the rotor frequency at the slip of 10 percent?

What is the rotor frequency at the slip of 10 percent?

A. 10 Hz
B.2 Hz
C. 5 Hz
D. 50 Hz


AnS:  fr = sf = 0.1*50
           fr = 5Hz

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A 4 pole D.C series motor at no load the speed will be

A 4 pole D.C series motor at no load the speed will be

A. 1500 rpm
B. 0 rpm
C. Very high
D. Vary between 1450 rpm to 1550 rpm.


Ans: Very high

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If the cross-sectional area of a magnetic field increases, but the flux remains the same, the flux density

If the cross-sectional area of a magnetic field increases, but the flux remains the same, the flux density

A. increases
B. decreases
C. remains the same
D. doubles

Explanatory answer : B


Flux density = flux / area

So if area increases, flux density decreases.

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When the speed at which a conductor is moved through a magnetic field is increased, the induced voltage

When the speed at which a conductor is moved through a magnetic field is increased, the induced voltage

[A] increases
[B] decreases
[C] remains constant
[D] reaches zero


Answer: A

In a generator induced emf is proportional to speed hence if speed increases,induced emf also increases.

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Which alternator more suitable for high-speed system ?

Which alternator more suitable for high-speed system ?

A. Salient pole

B. non salient pole

C. Both (a)& (b)

D. none of these

Answer: non salient pole, because salient pole alternators are mechanically weak.

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The equivalent circuit shown represents a / an ................. Gate.

The equivalent circuit shown represents a / an ................. Gate.

A. Ex-OR
B. NOT
C. OR
D. AND

Answer:

It is an AND gate because lamp glows only when both switches are closed.

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A resistance 5ohm inductance 0.02 H and capacitor 5 uf are connected in series.find the value of power factor at resonance condition.

A resistance 5ohm inductance 0.02 H and capacitor 5 uf are connected in series.find the value of power factor at resonance condition.

a. 0.6
b. 0.8
c. 0.9
d. 1

Answer:

at resonance condition,XL=XC and therefore Z=R, hence for pure resistive circuit pf will be unity.

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A 1-hp motor draws 1000 watts. What is its efficiency ?

A 1-hp motor draws 1000 watts. What is its efficiency ?


Answer:

Efficiency = output / input

Therefore, efficiency = 746 / 1000 = 0.746

Efficiency = 74.6 % 

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The eddy current loss in an a-c electric motor is 100 watts at 50 Hz. Its loss at 100 Hz will be

The eddy current loss in an a-c electric motor is 100 watts at 50 Hz. Its loss at 100 Hz will be

(A) 25 watts 
(B) 59 watts
(C) 100 watts 
(D) 400 watts

Explanatory answer:

Eddy current losses is proportional to square of frequency 
( f^2)

In thise case frequency is doubled, so the New loss proportional to (2f)^2

New loss is proportional to 4f^2

Eddy current loss at 100 HZ is = 4 times greater
                                                     =  400 watts

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