MCQs on Electric Circuits

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01․ Which of following is invariably seen in an electroplating plant?
Distilled water.
Carbon brushes.

In an electroplating plant, the DC power supply is used to do the electroplating operation. So, we can use DC generator (or) rectifier to get DC power supply from the conventional AC power supply. But, if we use the DC generator, the conversion efficiency is less and maintenance and initial cost are more. That is why most of the electroplating plant has the rectifier and we can invariably see it which is used to convert AC power supply into DC power supply.

02․ Electrics supply for electroplating should be
low AC voltage.
low frequency ac voltage.
DC voltage.
any of above.

In electroplating process, when more electrons flow into the piece, the metal particles in the object are removed from it. This operation happens by giving the positive direction of the power supply through the anode and cathode plates. Then, when the electrons are removed from the piece, the dissolved metal particle in the electrolyte sticks onto the working piece. This operation happens by giving the negative direction of the power supply through the anode and cathode plates. Thus, we need a constant single direction power supply at a time to do the above two operations. That is why the DC power supply is used in electroplating applications.

03․ Which law(s) find application in electrolysis?
Ohms law.
Gausss law.
Faradays law.
Coulombs law.

The Ohms law is used in resistance circuits. The Gauss's law and Coulombs law are used to find the electric field due to line charge. There are two different laws of faradays law that uses in the electrolysis process. The first law states that the amount of chemical change produced by an current in the electrode or electrolyte is directly proportional to the electricity used. The second law states that the amount of chemical changes produced by the same quantity of electricity in different substances is proportional to their equivalent weights.

04․ Silver coating is provided for
protective purpose.
decorative purpose.
bearing surfaces.
all of above.

Silver coating resists the corrosion affections in ferrite metals. So, it is used for protective purpose. The silver coating shows the clear and shiny at its outside surface. So, it is used for decorative purpose. The work piece surface is very smooth after finishing the coating. If we used this kind of surfaces in bearing application, the friction is very less. So, it is also used for bearing surfaces.

05․ Current efficiency in electroplating is usually
99 %.
90 to 98 %.
70 to 80 %.
50 to 60 %.

The current efficiency is the ratio of the weight actually deposited and the weight to be expected from Faradays laws. In the electroplating process, according to this statement the loss of efficiency is less because the input current does the electroplating process effectively without too much loss. It can maintain the current efficiency between 90 to 98 %.

06․ Aluminium is produced from bauxite by
electrolytic process.
froth flotation.

The mined bauxite is refined into alumina (Al2O3), and then it is converted into the metallic aluminium (Al) by the electrolytic process. In this process, the purified aluminium oxide is continuously fed into the tray. The mineral cryolite (Na3AlF6 - Sodium Hexa - fluoro - aluminate) is added at 500°C melting point and when the electric supply is passed between the positive and negative carbon tube, it dissolves the purified ore into Al3+ and O2 ions. Finally, the molten aluminium is deposited at the bottom of the tray and then it can be collected.

07․ Galvanizing is the coating of

Zinc is the only metal that is basically used to save the integrity of iron from the corrosion effects for a longer period of time. That is why zinc is coated on the surface of iron using galvanization process.

08․ Coating generally recommended for hard surfacing is
lead plating.
copper plating.
chromium plating.
none of the above.

Basically chromium plating is widely used in industrial based tools where there is no necessity of soft surfacing. The surface should be very hard for achieving the capability to do work with this kind of heavy tools in industries. This plating is also called as hard chrome plating.

09․ Highest current density is usually recommended for
tin plating.
cadmium plating.
bronze plating.
chromium plating.

Basically the chromium plating is the hard surface plating. For that, we need to generate the greater temperature to achieve the surface of the object as hard. So, it requires the highest current density such as 325 Amps / feet2 or 35 Amps / m2.

10․ Electro-chemical equivalent is usually expressed in
mg per volt.
mg per kVA.
mg per kW.
mg per coulomb.

As per the Faradays first law of electrolysis, the electro - chemical equivalent is the ratio of a mass of chemical deposition to the quantity of electricity. We know that the unit mass of chemical deposition is grams and the unit of quantity of electricity is coulomb. So, the unit of electro - chemical equivalent is milli - gram per coulomb.