Utilization of Electrical Energy- 1 - Free MCQ Practice Test with solutions,

Plastic or Non fusion welding: In this welding, the pieces of metal to be joined are heated to a plastic state and then forced together by external pressure. This procedure is used in forge welding, resistance welding, thermit welding and gas welding.

Fusion or Non pressure welding: In the fusion welding, the material at the joint is heated to a molten state and allowed to solidify. This includes gas welding, arc welding etc.

Cold welding: In this welding, the joints are produced without the application of heat but by applying pressure which results in inter-surface molecular fusion of the parts to be joined. This process is mainly used for welding nonferrous sheet metal.

The selection of proper welding depend on the following factors

1. The type of metal to be joined

2. The techniques of welding adopted

3. The cost of equipment used

4. The nature of products to be fabricated

In upset butt welding, the two metal parts to be welded are joined end to end and are connected across the secondary of a welding transformer

Due to the contact resistance of the metals to be welded, heating effect is generated in this welding.

The voltage required is 2-8 V and the current required ranges from 50 A to several hundred amperes depending upon material and the area to be welded at a time

Electric arc welding is the process of joining two metallic pieces. In this, melting of metal is obtained due to the heat developed by an arc struck between an electrode and the metal to be welded or between the two electrodes

When the supply is given across the conductors separated by some distance apart, the air gap present between the two conductors gets ionized. As the arc welding in progress, the ionization of the arc path and its surrounding area increases

The increase in ionization decreases the resistance of the path. Thus, current increases with the decrease in voltage of arc. It indicates that, arc has negative resistance characteristics

Drooping V-I characteristic is used on constant current type welding machine. When arc is struck in arc welding machine electoral is essentially in short circuit which would immediately require a sudden of current otherwise machine is designed to Prevent this. A constant current machine is designed to minimized these sudden surges.

In electric discharge lamps, a choke is connected in series with the supply to limit the starting current and to stabilize the arc.

Initially the sodium is in the form of a sloid, deposited on the walls of inner tube. When sufficient voltage is impressed across the electrodes, the discharge starts in the inert gas (neon). It operates as a low pressure neon lamp with pink colour

Group drives: Electric drive that is used to drive two or more than two machines from line shaft through belts and pulleys is known as group drive

Individual drive: A single electric motor is used to drive one individual machine.

Multi-motor drive: Several separate motors are provided for operating different parts of the single machine

For a paper mill requiring a constant speed operation and the flexibility of control we can use Individual or multi-motor drive

In the selection of the electric motor for a flour mill, starting torque and running torque both are important. Braking is least significant electrical characteristic for this purpose

Main line services: The distance between two stops is usually more than 10 km. High balancing speeds should be required. Acceleration and retardation are not so important

Urban service: The distance between two stops is very less and it is less than 1 km. It requires high average speed for frequent starting and stopping

Sub urban service: The distance between two stops is between 1 km and 8 km. This service requires rapid acceleration and retardation as frequent starting and stopping is required

In main line service, free running period is more. Hence Trapezoidal speed-time curve pertains to main line service

Average Speed: It is the mean of the speeds attained by the train from start to stop, i.e. it is defined as the ratio of the distance covered by the train between two stops to the total time of run. It is denoted with V_a

Average speed = distance between stops / actual time of run

V_a = D/T

Where V_a is the average speed of train in kmph

D is the distance between stops in km

T is the actual time in hours

Schedule Speed: The ratio of the distance covered between two stops to the total time of the run including the time for stop is known as schedule speed. It is denoted with V_s

Where T_s is the schedule time in hours

For a given value of an average speed, decrease in duration of stops causes increase in schedule speed

Dielectric heating has been applied in the food processing industry:

1. Dehydrating fruits, vegetables, eggs etc.

2. Cooking food without removing the outer shells

3. Pasteurizing milk and beer inside bottles

4. Defrosting frozen foods in large bakeries and restaurants

Electric resistance heating furnace is used for cremation purpose

The power factor will be maximum in case of resistance heating compared to any other heating method

Dielectric loss is

P_L= V²_ωCδPL = V²ωCδ

Where, V is the applied voltage in V

f is the supply frequency in Hz

C is the capacitance

δ is the loss angle in radian

Dielectric loss is directly proportional to the square of the voltage impressed on the dielectric

The supply frequency usually employed for high frequency eddy current heating is 10-400 kHz

The supply frequency usually employed for dielectric heating is 1-40 MHz

Electrodeposition: It is the process by which one metal is deposited over other metal or non-metal by electrolysis

Electro metallization: It is the process by which the metal can be deposited on a conduction base for decoration and for protective purposes. Any non-conductive base is made as conductive by depositing graphite layer over it

Electro facing: It is the process of the coating of a metallic surface with a harder metal by electrodeposition

Anodizing: The process of deposition of oxide film on a metal surface is known as anodizing and oxidation

The filtration of electrolyte is necessary to remove the suspended salt particles and the other suspended impurities from the electrolyte