Battery: Cell & Batteries MCQs with Explanatory Answers

Answer:      ( 1 )

An electrolyte cell consists of a positive electrode and a negative electrode separated from each other by an electrolyte. The electrolyte can be concentrated aqueous solutions like acids, alkalis or salts, or ionic conductors like organic salt solutions, polymers, ceramics etc. The electrolyte is a good conductor of ions, but a bad conductor of electrons. Two or more such cells connected together in series or in a series-parallel array forms an assembly called Battery.

Answer:      ( 1 )

In a single electrolytic cell, the positive electrode and negative electrode have minimum distance between them, about 1mm, so that the internal resistance is as low as possible. Typical value of this resistance is of the order of mill-ohms, so that voltage drops between the electrodes is minimum when drawing huge amount of current

Answer:     ( 2 )

The net voltage or voltage difference between potentials of the positive and negative electrodes of a electrolyte cell defines the open circuit voltage at standard conditions. During discharge of the battery, the negative electrode undergoes oxidation while the positive electrode undergoes reduction as given below:

Thus, open circuit voltage at standard conditions is: V^o = E^o1-E⁰² = +1.690 – (-0.358) Volts = +2.048 Volts

Answer:       ( 1 )

Consider a primary cell having Zinc electrode as negative electrode and Carbon electrode as negative electrode and Sulfuric acid as the electrolyte. Movement of electrons from negative electrode to the positive electrode constitutes current flow through the load. The chemical reaction that takes place ensures that the positive ions in the Zinc electrode combines with the negative ions from the Sulfuric acid, forming Zinc Sulfate.

Thus, as the reaction proceeds further, Zinc gradually dissolves into the solution, causing the cell to be discharged. This proves that in a primary cell, one of the electrodes is used away with the chemical action

Answer:      ( 1 )

Consider a 12-Volt Lead-Acid battery having fully charged terminal voltage of 12.6 Volts. When the battery is supplied with an external voltage greater than the terminal voltage, smooth charging is ensured.

As electricity passes through the electrolyte solution, the Lead Sulfate at the electrodes converts back to its original substance, i.e. anode or positive plate of Lead Dioxide and Cathode or negative plate of Sponge Lead.

Answer:      ( 2 )

A primary dry cell, also known as Leclanche cell, consists of a moist paste as its electrolyte. The paste is usually a mixture of substances like ammonium chloride, manganese dioxide, powdered coke, graphite and water.  The paste is contained in a Zinc container, which acts as the cathode or the negative electrode. The container is lined with a non-conducting material to separate Zinc from the paste.

Answer:      ( 4 )

Nickel Cadmium cells contain Cadmium Hydroxide as cathode, Nickel Hydroxide as anode and Potassium Hydroxide and water as electrolyte. Though Nickel-Cadmium batteries are comparable with Lead-Acid batteries at normal discharge rates, at higher discharge rates, the amount of power delivered is higher in the former. Also, Ni-Cd batteries show superiority over Lead-Acid batteries in terms of faster charging rate, less time to charge, longer storage period and longer intervals of charging and discharging.

Answer:     ( 2 )

Consider the below series combination of four cells.

Figure 1: Series Connected Cells

Notice that the negative electrode of each cell is connected to the positive electrode of its adjacent cell. If voltage across each cell is V volts, the total voltage across the loop will be determined using Kirchhoff’s law as sum of the individual voltages across each cell. Hence total voltage will be 4V volts. This shows that cells connected in series provides a higher voltage.

Answer:     ( 1 )

Consider the below parallel combination of four cells.

Figure 2: Parallel Connected Cells

Note that positive electrodes of all the cells are connected in series with each other and the negative electrodes are connected in series with each other. This ensures that voltage across the combination is same as the voltage across a single cell, i.e. V volts. However, the total current flowing would be sum of the individual currents flowing through each cell. Thus, cells connected in parallel constitute flow of higher current.

Answer:     ( 2 )

Specific Gravity of a substance is defined as the ratio of its weight compared to the weight of same amount of pure water. This term is used to determine the amount of active ingredient in an electrolyte, to ensure smooth operation of the cell. Since the electrolyte is a solution of water, the amount of active ingredient cannot be measured directly.

Any substance which floats on water will have specific gravity less than that of pure water, i.e. less than 1.0. Since the active ingredient used must sink or dissolve in water, the specific gravity is usually greater than that of pure water, i.e. greater than 1.0.

Answer:     ( 3 )

Theoretically, capacity or rating of a storage battery is given in terms of the total amount of current which flows through the battery, at a given amount of time and is a constant value. However, practically the rating depends upon the rate of discharge and the ambient temperature. Higher the rate of discharge, lesser will be the capacity.

The discharge occurs till the voltage per cell reduces to 1.7 volts, especially for Lead-Acid batteries. For a storage battery rated 100 Ampere-Hours at 5-Hour discharge rate, if the latter is decreased to 30-minute rate, the capacity delivered will be 1/3^rd of the given nominal capacity. If the discharge rate is increased to 10-Hour rate, the capacity delivered will increase by 20% than the nominal value.

Also, optimal battery performance is achieved in the working temperature range from 20 degree Celsius to 30 degree Celsius. According to few practical tests, discharge rate of battery doubles with every 10-degree Celsius rise in temperature. Though at higher temperature, the rate of occurrence of chemical reactions will be faster, the life of the battery will be reduced.