Engineering MCQ's.🎓

            Basic concepts related to AC circuit :- Reactance : -      Reactance is defined as the opposition produced in ac circuit by reactive element auch as capacitor or inductor. It is mejores by ' X ' and its unit is ' ohm '. The reactance is devided into two parts:- Inductive reactance (XL). Capacitive reactance (XC).  Inductive reactance (XL) :-          Inductive reactance is defined as opposition produced in ac circuit by inductor.                       XL = 2πFL Its unit is ohm 2. Capacitive reactance (XC) :-          Capacitive reactance is defined as opposition produced in ac circuit by capacitor.                     XC  = 1/2πFC It's unit is also ' ohm '. Impedance :-      Impedance is defined as opposition produced by combination of resistance and reactance in ac circuit. It's unit is ' ohm '                     Z  = √ R^2 + X^2 Types of power :- Real or true or active power (P). Reactive or imaginary power (Q). Appearent power (

Transformer :-     Transformer is static device or which transfers AC power from one circuit to another without change in frequency. The main parts of transformer are as follows:-  Three limb core. LV winding. HV winding. Tapped winding. Tap leads. LV bushings. HV bushings. Frame. ON load tap changer. Conservator tank. Radiator. Breather. Test valve. Temperature and oil level indicators. Buccholz relay.   We transformer there is no change on frequency from No load to full load. The voltage level can be changed either it stepped up or down according to need. The transformer is very crucial device in electrical system now days, Without it we can't run our system efficiently. There are two main type of transformer:-  1. Power transformer. 2. Distribution transformer. Other some special types of transformer are there used for special purpose only like, isolation transformer, instrument and welding transformer etc.

  ● Did you know why insulators are in our electrical system ?     The insulator is a very crucial part of our electrical system. It is used  for safety to separate two energised or non energised parts of electrical equipment or in transmission and distribution system.      The most important role of insulators in generation, transmission and distribution. This insulators mainly made up of  porcelain.  Insulators are used in electrical equipment to support and separate electrical conductors without allowing current through themselves.        An insulating material used in bulk to wrap electrical cables or other equipments is called indulation. The term insulator is also used more specifically to refer to insulating supports used to attach electric power distribution or transmission lines to utility poles and transmision towers.     They support the weight of the suspended wires without allowing the current to flow through the tower to ground.    The different insulators are used for di

Air conditioner: Q.- Why air conditioners rated in tones? Ans-  Why AC rated in Tons capacity instead of kW because AC are designed on the basis of amount of heat removal from particular area or hall . 1000 Kilocalories or 4120 kilojoules or 12000 BTU equal to one Ton of heat. Quantity of heat is termed in Tons means if an air conditioner is able to remove 1000 kilocalories of heat or 4120 kilojoules or 12000 BTU of heat in an hour that AC rated as 1 Ton of AC. Also, this is the same case for freezer and refrigerator i.e. refrigeration system. where, BTU = British thermal unit. A measurement of heat, specifically, the amount of heat needed to raise the temperature of a pound of water by 1° 1 Ton =12,000 BTU/h1 Watt =3. BTU/h 1 Ton =12,000 /3. =3,516.8528 Watts =3.5168528 kW. 1 Ton =3,516.8528 Watts = 3.516 kW. A Ton of refrigeration (RT) is approximately equivalent to 12,000 BTU/h or 3,516.8528 W or 4.7142Hp. A Ton of refrigeration (RT) is a unit of power used to describe the heat-extr

Q - Why induction motor is self starting and synchronous motor is not ? Ans_    A 3- phase supply given to the armature of Induction Motor produces a rotating magnetic field. This rotating magnetic field rotates at synchronous speed Ns = (120xf)/P This rotating magnetic field links to the rotor coils and induces voltage which in turn produces current in the rotor. The current carrying rotor being placed in a magnetic field experiences a torque and hence begins to rotate in the direction of rotating magnetic field. Thus we see that Induction Motor is self-starting. It does not require nay external mean to rotate. Now we consider a 3-phase synchronous motor. A 3-phase supply is given to the armature of Synchronous Motor, produces a rotating magnetic field. However, in this case, the rotor has its own field produced by a DC current flowing through the rotor winding. This rotor field tends to align itself along with the rotating magnetic field produced by the stator i.e. armature winding.

                              Electric stairs (escalators): Q.-Why electric stairs or escalators uses DC motors instead AC? Ans_         DC compound motors are used in elevators. A DC compound motor can be called as a superimposition of DC series and DC shunt motor. So, it has high starting torque like a DC series motor and has better control of speed like a shunt motor. Both these features make it ideal to be used in lifts where the lift needs to break high stall torque and also needs efficient speed control over its operation - be it travelling one floor or 50 floors at a time. The compound motor responds better to heavy load changes than a shunt motor because of the increased current through the series field coils. This boosts the field strength, providing added torque and speeds. Thus, DC compound motor satisfies the load and operational requirements to be used in an elevator and is the most sought for.