15 March 2020

Batteries Interview Question Answer - 1


1
Describe the function of the electric primary cell.


Function of electrical cell
  • The function of the electric cell is to convert chemical energy into electrical energy.


2
How does the primary cell produce electrical energy?


Primary Cell
  • The electrical cell consists of two metal electrodes and electrolytes ( chemical ).
  • When the metal electrode is placed in the electrical conducting solution ( electrolytes ), the atoms at the metal surface tends to exchange its electrons with the electrolytes and becomes charged in this process.
  • Some of these charged electrons or ions tend to leave the metal and wander in the electrolytes.
  • This tends to set up a small voltage difference between the electrode and electrolyte.
  • This value of electrode potential is not same for all metal but its value varies from metal to metal.
  • The copper, mercury and silver develop positive voltage whereas metal like lithium and zinc develops a negative voltage.
  • When two electrodes placed in the electrolyte, the process of oxidation and reduction take place.
  • The potential is developed between two electrodes due to this process.


3
What is meaning of the oxidation and reduction?


Oxidation and reduction
  • The term oxidation means atoms losing electrons.
  • The process of oxidation occurs at one electrode which gain electrons from electrolyte and this metal electrode become negative charged i.e. negative electrode
  • Whereas the reduction occurs at the other electrode which loses electrons to ions in the electrolyte therefore this electrode becomes positive charged i.e. positive electrode


4
Explain : Primary cell and Secondary cell


Primary cell
  • The electrical cells which are not rechargeable are called as primary cells.

Secondary cell
  • The electrical cells in which charging is reversible is called as secondary cells.


5
Why the rating of the primary cell is not given in ampere - hours?


Rating of the primary cell
  • The efficiency of the primary cell drops as the higher currents are drawn from them.
  • The electro – chemical reaction in the primary cell slow down at low temperatures resulting ability of the cell reduce to deliver electrical energy.
  • Therefore the manufacturers do not given the primary cell rating in the ampere - hours or milli amp hours.


6
Describe the effect of temperature on the primary cells.


Effect of temperature on the primary cell
  • The chemical reaction slow down in the many primary cells and batteries slow down particularly at lower temperature.
  • The internal chemical activity speed up sufficiently to cause the cell to discharge itself and loses its capacity at the temperature above 500 C. 
  • Therefore they should not be stored at higher temperature.


7
Which are the common sizes of the primary cells?


The primary cells are available in the sizes of D cell, C cell, AA cell, AAA cell.

8
State the different types of the primary cells.


The following are the commonly used primary cells.
  • Zinc – mercury oxide : 1.35 V button sizes
  • Zinc – oxygen : 1.45 V button and pill sizes
  • Carbon – zinc : 1.5 V
  • Zinc chloride : 1.5 V
  • Zinc – silver oxide : 1.5 V
  • Lithium – manganese dioxide : 3.0 V


9
Why the primary cells are not rechargeable?


Primary cells
  • There are many primary cells contain highly corrosive electrolytes like potassium hydroxide, toxic materials such as mercuric oxide, highly reactive materials like lithium which can be explode on contact with water.
  • Therefore it should be taken great care while disposing it. Therefore the primary cells are not designed to be rechargeable, attempt to do it recharge may result exploding.


10
Describe the function of electrolyte in the secondary cell.


Function of electrolyte
  • When current is passing through electrolyte chemical action takes place and it converts electrical energy into chemical energy during charging and chemical energy into electrical energy during discharging.


11
State the different types of secondary ( Rechargeable ) cell.


There are following types of rechargeable cells
  • Sealed lead acid  ( SLA )
  • Rechargeable alkaline – Manganese ( RAM )
  • Lithium – Iron ( Li – ion )
  • Nickel – Metal hybrid ( Ni – MH )
  • Nickel – Cadmium ( Ni – cad )


12
Explain the term : Capacity of cell


Capacity of the cell
  • The capacity of the cell is given in the Ah ( ampere – hour ) or mAh ( milli – ampere hour ).

      1 Ah =  ( 1.0 coulomb / sec ) × hour
              =  ( 1.0 coulomb / sec ) × 3600 Second
              =  3600 coulombs

13
Describe the significance of term ‘energy density’ in the secondary cells?


Energy density
  • The energy density of the cell is specified in watt-hours per kilo – gram ( Wh / kg ).
  • It signifies that how much electrical energy can be stored per kilo – gram of cell weight.
  • The energy density of the each cell is not same. The value of energy density for ( 1 ) Lead – acid cell : 30 Wh / kg ( 2 ) Nickel – metal hybrid : 80 Wh / kg and ( 3 ) Lithium – iron : 140Wh / kg etc.


14
What is meaning of the term ‘C rate’?


C rate
  • The cell is charged and discharged at different current rates. These rates are usually specified in terms of ‘C rate (current rate)’, where C is the cell’s nominal capacity in Ah or mAh.
  • 1C means - cell is discharged at the same rate as its nominal capacity therefore it takes one hour before it normally discharged.
  • 0.5 C -  Nominal charge should last for two hours
  • 0.05 C -  Nominal charge should last for twenty hours
  • 2 C -  Nominal charge should last for thirty minutes


15
Describe the meaning of discharge of  : 1.4Ah battery at 1C rate , 1.4Ah battery at 0.5C rate and 1.4Ah battery at 2.0C rate


( a ) 1.4 Ah, 1.0 C
  • It means that 1.4 Ah battery would be delivering 1.4A for one hour.

( b ) 1.4 Ah, 0.5 C
  • It means that 1.4 Ah battery would be delivering 1.4 A for two hour.

( c ) 1.4 Ah, 2.0 C
  • It means that 1.4 Ah battery would be delivering 1.4 A for thirty minutes.


16
What is importance of the value of C rate of different charging level?


The value of C rates is used to describe charging as well as discharging conditions.
  • Fast charging : > 0.5 C
  • Normal charging : 0.2 C to 0.5 C
  • Trickle or slow charging : 0.05 C to 0.2 C


17
Describe the effect on cell performance of fast charging and slow charging.


Effect of fast and slow charging
  • The fast charging or discharging generate more heat inside the cell therefore it will reduces cell’s effective capacity.
  • The slow charging or discharging can give lower effective capacity due to fact that all batteries suffer from internal self discharging effects.


18
Which parameters greatly affect the emf of the cell?


The magnitude of the emf of the cell depends upon
  • Material of the electrodes and
  • Type of the electrolyte material


19
Describe the difference between battery and cell.


Battery and cell
  • The term cell and battery are not interchangeable.
  • The cell is single unit of battery which consists of two electrodes and electrolyte while the battery consists of group of interconnected cells.


20
Which type of chemical action taken place during charging and discharging of the cell?


Charging
  • The electrical energy is converted into chemical energy.

Discharging
  • The chemical energy is converted into electrical energy.




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