Quiz: Electrical Engineering
Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute
Q1. In a four-pole D.C. machine:
(a) all the four poles are north poles
(b) alternate poles are north and south
(c) all the four poles are south poles
(d) two north poles follow two south poles
Q2. The field coils of DC generator are generally made up of:
(c) Cast Iron
Q3. The basic requirement of a d.c. armature winding is that it must be………
(a) a lap winding
(b) a closed one
(c) a wave winding
(d) either ‘a’ or ‘c’
Q4. The brushes of a dc machine are made of:
Q5. To convert a galvanometer into voltmeter, the value and type of connection of the resistance to be connected with should be
(a) Low and parallel
(b) High and parallel
(c) Low and series
(d) High and series
Q6. A voltmeter must have a very high internal resistance so that the:
(a) accuracy is high
(b) resolution is high
(c) meter draws minimum current
(d) loading is maximum
Q7. Which starting method is not used in squirrel cage induction motors?
(a) Resistance in rotor circuit
(b) Resistance in stator circuit
(c) Auto-transformer starting
(d) Star delta starting
Q8. What is condition for maximum starting torque of three phase induction motor if R₂ and X₂ are rotor resistance and reactance respectively?
(a) R₂ = 0, X₂ = 1Ω
(b) R₂ = 2 X₂
(c) R₂ = 0.5 X₂
(d) R₂ = X₂
Q9. The supply voltage to an induction motor is reduced by 10% By what percentage, approximately, will the maximum torque decrease?
(d) None of the above
Q10. Insulation resistance of a cable of length 20 km is 2 MΩ. What will be the insulation resistance of the same cable but for a length of 200 km?
Sol. alternate poles are North-south or South-north
Sol. because copper is an excellent conductor and becomes electromagnet when current passing through it.
Sol. a closed one
Sol. The brushes can be made of carbon or copper, but the resistance of the carbon brushes allows less current inrush during commutation between adjacent commutator segment.
Sol. A galvanometer is very sensitive instruments so it can’t measure low value of current A Galvanometer can be converted into voltmeter by connecting a high resistance in series with it.
Sol. A voltmeter having very high resistance so that if will draw minimum current and drop will be negligible and will correctly measure the CKT voltage.
▭(Rseries=Rm (m-1) ) when(m=I/Im or V/Vm )
Sol. Rotor resistance starting is used only for slip-ring induction motor because rotor of squirrel cage induction motor is short circuited.
Sol. Starting torque (Ts)= (KR₂)/(〖R₂²〗^ +x₂²) (Here S=1)
For maximum value (d(Ts))/(dR₂)= 0
⇒ R2=x₂ → condition for maximum starting torque.
Sol. For Induction motor: –
If V is reduced by 10% then
So, % change = (V^2-(0.9v)²)/V²×100
Sol. insulation resistance of cable ⍺ 1/ length