List of practice Questions

Choose a wrong choice on d.c. machine regarding compoles or compensating winding
Swinburne’s test measures the following on a 200 V, 15 kW dc shunt motor:
Input current = 7 A; Field current = 2 A. Estimate field copper loss and iron \& frictional losses. Assume \( R_a = 0.04 \Omega \)
The current and power factor of a 3–\(\phi\) induction motor at no-load are respectively
A 3-\(\phi\), 400 V, 50 Hz, 4 pole induction motor has rotor resistance and standstill reactance of 0.08 Ω and 0.4 Ω respectively. What is its approximate speed at maximum torque?
The external rotor resistance of a 3-\(\phi\) induction motor is increased more than the resistance required to get maximum starting torque. Then maximum torque occurs in \underline{\hspace{2cm} of Torque (y-axis) – Speed (x-axis) characteristic plot.
A 1-\(\phi\), 230 V, 50 Hz transformer is operated at 230 V, 60 Hz. Then its
Indicate a correct choice on currents during open circuit (OC) and short circuit (SC) tests of transformer
A 11kV/3.3kV, 100 MVA, 3-phase transformer has equivalent impedance seen from LV side of (1.2 + j4.8) Ω. The per unit impedance of the transformer is
If R and X are equivalent resistance and equivalent reactance of a transformer respectively, then at maximum voltage regulation, the power factor is
Two identical coaxial circular coils carry the same current 1 amp but in opposite directions. The magnitude of the magnetic field \( B \) at a point on the axis midway between the coils is
Magnetic dipole moment is ______ of the loop, its direction is normal to the loop
\( \nabla \cdot \vec{B} = 0 \), shows that
The reciprocal of reluctance is
The magnetization \( M \), in amperes per meter is
The slip-speed of a 3-\(\phi\), cage, 50 Hz, induction motor is 20 rpm at no-load. If slip-speed is doubled due to load, then the electrical equivalent of mechanical load will
Choose the correct statement of Reciprocity theorem in single source network:
If BW is bandwidth, \( \omega_r \) is resonant frequency and Q is quality factor of a resonant circuit, then Selectivity is defined as:
The response of a 1-$\phi$ R-L series circuit is \( i(t) = Ae^{-\frac{R}{L}t} + I_m \sin(\omega t - \theta) \). Then the supply voltage should be:
Point charges \( Q_1 = 1\text{nC} \) and \( Q_2 = 2\text{nC} \) are at a distance apart. Which of the following statement is \textbf{incorrect?
If \( \vec{D} = \epsilon \vec{E} \) and \( \vec{V} = \sigma \vec{E} \) in a given material, the material is said to be:
A source voltage of 100 V dc is applied across a RLC series circuit. Under steady-state conditions, voltages across each element is
The equivalent inductance of two equal inductances when connected in series aiding is 14 H and when connected in series opposing is 6 H. What is the coefficient of coupling?
Certain resistors connected in parallel and the equivalent resistance is \( X \). If one of the resistances is removed the equivalent resistance is \( Y \). What is the conductance value of removed resistance?
A signal of \( v = 5 + 10 \sin \omega t \) is applied across a \( 2\, \Omega \) resistor. The power dissipated in the resistor is
Three impedances \( 6 + j(10/3)\, \Omega \) each are connected in delta. The per-phase impedance of equivalent star circuit will be