Each question carries 1 mark.
Negative marking: 1/4 mark
Total Questions: 06
Time: 08 min.
Q1. The rotor input when rotor copper loss in an induction motor is 600 W and slip 3 % is:
(a) 18 kW
(b) 20 kW
(c) 25 kW
(d) 200 kW
Q2. The mutual inductance between two coils having self -inductances 3 H and 12 H and coupling coefficient is 0.85:
(a) 1.7 H
(b) 5.1 H
(c) 12.75 H
(d) 0.425 H
Q3. In a 3-phase induction motor, the mechanical power developed, in terms of air gap power P_g is:
(c) (1-s) P_g
Q4. In the given circuit, if the power consumed by 5Ω resistor is 10 watts, then power factor of the circuit is
Q5. In residential wiring in practice for earthing the following method is adopted……
(a) Resistance earthing
(b) Neutral earthing
(c) Pipe earthing
(d) Plate earthing
Q6. For which of the following is magnetic susceptibility negative?
(a) Paramagnetic and Ferromagnetic materials
(b) Paramagnetic Materials only
(c) Ferromagnetic Materials only
(d) Diamagnetic Materials
Sol. Pcu = Rotor copper loss = sP_g
Where; P_g=air-gap power or rotor input power
∴P_g=600/0.03=20000 W=20 kW
Sol. M=k√(L_1 L_2 )=0.85×√(3×12)=0.85×6=5.1 H
Sol. In residential wiring in practice for earthing, plate earthing is adopted.
• In Plate Earthing an earthing plate either of copper of dimension 60cm×60cm×3m of galvanized iron of dimensions 60 cm× 60 cm×6 mm is buried into the ground with its face vertical at a depth of not less than 3 meters from ground level.
Sol. Diamagnetic material: Magnetic materials which align against the magnetic field are known as diamagnetic materials. Magnetic susceptibility is χ<0 which means it is always a negative value for diamagnetic material.
These materials are independent of temperature. As these materials magnetize in the opposite direction, they do have a small amount of magnetization intensity. Gold, tin, mercury, water, etc are examples of diamagnetic materials.
For a diamagnetic material, the relative permeability lies between 0 ≤ μr < 1 and its susceptibility lies between −1< χ< 0. 𝑥=𝑢𝑟−1
Where 𝑥 is a dimensionless quantity defines as the magnetic susceptibility of the medium.