Tag: electricity

We know that the current flows from positive electrode to negative electrode in a cell. The direction of electrons is always opposite to the direction of the current. Thus, the electrons move from negative electrode to positive electrode.  

The e.m.f of a Daniel cell always remains constant and is equal to $1.08$ volts.

When an external circuit is connected across the cell, electrons flow from negative electrode to positive electrode(current flows opposite to this) in the external circuit. Inside the cell, negatively charged ions are attracted to negative electrode because it is depleted of electrons. Similarly, inside the cell, positively charged ions are attracted to positive electrode. 

A common dry cell is zinc-carbon cell with a normal voltage of 1.5 V , same as the alkaline cell.

A battery converts chemical energy into electrical energy.

Dry cell being primary cell, cannot be recharged.
Acids cell are used as car batteries.
The nickel-iron battery (Ni-Fe battery)( also called Edison Cell)  is a rechargable battery having nickel(III) oxide-hydroxide positive plates and iron negative plates, with an electrolyte of potassium hydroxide. It is a very robust battery which is tolerant of abuse, (overcharge, overdischarge, and short-circuiting) and can have very long life even if so treated.

The battery made by Volta is credited as the first electrochemical cell. It consists of two electrodes: one made of zinc, the other of copper. The electrolyte is either sulfuric acid mixed with water or a form of saltwater brine.

The chemical action that occurs in the cell while the current is flowing causes hydrogen bubbles to form on the surface of the anode. This action is called POLARIZATION. Some hydrogen bubbles rise to the surface of the electrolyte and escape into the air, some remain on the surface of the anode. If enough bubbles remain around the anode, the bubbles form a barrier that increases internal resistance. When the internal resistance of the cell increases, the output current is decreased and the voltage of the cell also decreases.

Voltaic cell has a lot of polarization due to ongoing reactions.Daniell cell is an improvement on the voltaic cell using two electrolytes and solves the problem of polarisation.

The charging of all secondary batteries are based on conversion of electric energy to chemical potential energy with the user of battery charger. The negative terminal of the cell has to be connected to the negative terminal of the voltage source and the positive terminal of the voltage source with the positive terminal of the battery. Further, the voltage output of the source must be higher than that of the battery, but not much higher: the greater the difference between the power source and the battery's voltage capacity, the faster the charging process, but also the greater the risk of overcharging and damaging the battery.