Engineering MCQ's.🎓

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.

Basic electrical terms. Alternating Current (AC)  — An electric current that reverses its direction many times a second at regular intervals. Ammeter  — An instrument for measuring the flow of electrical current in amperes. Ammeters are always connected in series with the circuit to be tested. Ampacity  — The maximum amount of electric current a conductor or device can carry before sustaining immediate or progressive deterioration. Ampere-Hour (Ah)  — A unit of measure for battery capacity. It is obtained by multiplying the current (in amperes) by the time (in hours) during which current flows. For example, a battery which provides 5 amperes for 20 hours is said to deliver 100 ampere - hours. Ampere (A)  — A unit of measure for the intensity of an electric current flowing in a circuit. One ampere is equal to a current flow of one coulomb per second. Apparent Power  — Measured in volt-ampers (VA). Apparent power is the product of the rms voltage and the rms current. Armature  — The mova

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