Ques 31. The rating of fuse is expressed in terms of
Amperes✔
Volts
VAR
KVA
Fuses are ‘overcurrent protection devices’ and therefore will be rated in current units, i.e. Amperes. A fuse opens or “blows” and opens the circuit when the current (amperes) exceeds a preset limit.
Ques 32. The material commonly used for sheaths of underground cable is
Lead✔
Steel
Rubber
Copper
The insulator conductors are covered with the lead sheath. This provides additional mechanical strength and also protects the cable from moisture.
Note: The most common material used as the sheath in today’s cables is Poly-Vinyl-Chloride or PVC. In earlier days, the lead was used as the sheath.
Ques 33. The ratio of line-to-line capacitance and line to neutral capacitance is
1/2✔
1/4
2
4
CL-L = Capacitance between line to
Where D = Distance between the conductor
r = radius of the conductor
CL-L/CL-N = 1/2
Ques 34. The response of a network is decided by the location of
Zero
Poles
Both zero and pole✔
None of the above
The response of a network is decided by the location of both zero and pole
The poles decide the number of terms in impulse response and their complex frequency.
The zeroes along with poles and gain factor decide the amplitude of each impulse response term.
A Maxwell bridge is a modification to a Wheatstone bridge used to measure an unknown inductance (usually of low Q value) in terms of calibrated resistance and inductance or resistance and capacitance.
Hay’s bridge is a modification of Maxwell’s bridge. Hay’s bridge uses a resistor in series with a standard capacitor (unlike Maxwell’s bridge which uses resistance in parallel with the capacitor). The Hay’s bridge is suited for the measurement of high Q inductors, mostly those inductors having Q > 10.
Ques 36. A 1-Φ induction motor is running at N-rpm. Its synchronous speed is Ns. If its slip with respect to forward field is s, what is the slip with respect to the backward field?
s
-s
(1 – s)
(2 – s)✔
Slip with respect to forward field
S = (Ns – N)/Ns = 1 – N/Ns
Since the backward rotating flux will rotate opposite to the stator hence the sign rotor speed N will be changed
Sb = (Ns – [-N])/Ns = 1 + N/Ns
Adding both the equation
S + Sb = (1 – N/Ns) + (1 + N/Ns)
Sb = 2 – s
Ques 37. A polynomial q(s) is Hurwitz if
q(s) is real when s is real
q(s) is real and have real roots which are zero or negative✔
q(s) has a conjugate pair of complex roots
q(s) is an imaginary pair of complex roots
One of the properties of Hurwitz is that the real part of every root should be either zero or negative.
Ques 38. In Lap winding, the number of brushes is always
Double the number of poles
Same as number of poles✔
Half the number of poles
Multiple of number of poles
In a lap winding, the number of parallel paths, a, is always equal to the number of poles, p, and also to the number of brushes.
Ques 39. When the frequency of the source voltage decreases, the impedance of a parallel RC circuit.
Increase
Decrease✔
Remain Same
Decrease to zero
In parallel circuit
1/Z = 1/R + 1/Xc.
Since Xc = 1/(2πfc) which is Xc is inversely proportional f.
Thus in the parallel circuit the higher the resistance the lower the total resistance(impedance) therefore if the frequency decrease, the impedance will be decreased.
Ques40. When the number of poles and number of armature conductors are fixed in the D.C generator then which winding will give Higher EMF?
Wave Winding✔
Lap Winding
Either Lap or Wave Winding
Depend upon the conductor
E.M.F Equation of d.c generator is
Now for Lap wound generator A = P
Where
A = Number of parallel path
P = Number of poles
Therefore in Lap wound D.C generator they canceled each other.
For Wave wound Generator A = 2
Therefore the E.M.F is greater in Wave wound D.C generator than Lap wound
