Sources of Electric current - Electro chemical cells or electric cells

Sources of Electric current - Electro chemical cells or electric cells

An electric cell is something that pro- vides  electricity to different devices that are not fed directly or easily by the supply of electricity.

ACTIVITY 2

Shall we produce electricity at our home?

Materials required:

Zinc and copper electrodes, a light blub, connecting wires, and fruits such as lemons, orange,apples, grapes, and bananas.

Procedure:

1. Set up a circuit as shown in figure

2. Note the brightness of the blub when the circuit is connected to a lemon.

3. Repeat the experiment using the other fruits listed above. Do you notice the differences in the brightness of the bulb when it is connected to different fruits? Which fruit gives the greatest brightness? Why? (If you do not know please get the appropriate reason from your teacher)

Inference:

In the above activity what makes enabled the bulb to glow. Why there is a difference in the brightness of the bulb? The reason is that the fruits  which you have connected to the bulb produces the electric energy at different levels

The sources which produce the small amount of electricity for shorter periods of time is called as electric cell or electro chemical cells. Electric cell converts chemical energy into electrical energy

In addition to electro chemical, we use electro thermal source for generating electricity for large scale use.

It has two terminals. When electric cells are used, a chemical reaction takes place inside the cells which produces charge in the cell.

1. Types of cell – primary cell and secondary cell

In our daily life we are using cells and batteries for the functioning of a remote, toys cars, clock, cell phone etc. Event hough all the devices produces electrical energy, some of the cells are reusable and some of them are of single use. Do you know the reason why? Based on their type they are classified into two types namely – primary cell and secondary cell.

Primary cell

The dry cell commonly used in torches is an example of a primary cell. It cannot be recharged after use.

Secondary cells

Secondary cells are used in automobiles and generators. The chemical reaction in them can be reversed, hence they can be recharged. Lithium cylindrical cells, button cells and alkaline cells are the other types that are in use.

ACTIVITY 3

I am so exhausted. I am going to faint. What first aid will you give me to wake up?

I'll recharge the secondary cell by connecting it to an electrical circuit. 

2. Difference between primary cell and secondary cell

PRIMARY CELL

1. The chemical reaction inside the primary cell is irreversible

2. It cannot be recharged.

3. Examples of secondary cells are lead accumulator, Edison accumulator and Nickel – Iron accumulator.

4. Examples- simple voltalic cell, Daniel cell, and lechlanche cell and dry cell

SECONDARY CELL

1. The chemical­reaction inside the secondary cell is reversible

2. It can be recharged

3. It is used to operate devices such as mobile phones, cameras, computers, and emergency lights.

4. Examples of secondary cells are lead accumulator, Edison accumulator and Nickel – Iron accumulator.

3. Primary cell – simply Dry cell

A dry cell is a type of chemical cell commonly used in the common form batteries for many electrical appliances. It is a convenient source of electricity available in portable and compact form. It was developed in 1887 by Yei Sakizo of Japan.

Dry cells are normaly used in small devices such as remote control for T.V., torch, camera and toys.

A dry cell is a portable form of a leclanche cell. It consists of zinc vessel which acts as a negative electrode or anode. The vessel contains a moist paste of saw dust saturated with a solution of ammonium chloride and zinc chloride.

The ammonium chloride acts as an electrolyte.

Electrolytes are substances that become ions in solution and acquire the capacity to conduct electricity.

The purpose of zinc chloride is to maintain the moistness of the paste being highly hygroscopic. The carbon rod covered with a brass cap is placed in the middle of the vessel. It acts as positive electrode or cathode.

It is surrounded by a closely packed mixture of charcoal and manganese dioxide (MnO₂) in a muslin bag. Here MnO₂ acts as depolarizer. The zinc vessel is sealed at the top with pitch or shellac. A small hole is provided in it to allow the gases formed by the chemical action to escape. The chemical action inside the cell is the same as in leclanche cell.

The dry cell is not really dry in nature but the quantity of water in it is very small, as the electrolyte is in thefrom of a paste. In other cells, the electrolyte is usually a solution

4. Batteries

Batteries are a collection of one or more cells whose chemical reactions create a flow of electrons in a circuit. All batteries are made up of three basic components: an anode (the ‘+’ side), a cathode (the ‘–’ side), and some kind of electrolyte. Electrolyte is a substance that chemically reacts with the anode and cathode.

5. Invention of the Battery

One fateful day in 1780, Italian physicist, physician, biologist, and philosopher, Luigi Galvani, was dissecting a frog attached to a brass hook. As he touched the frog’s leg with an iron scapel, the leg twitched.

Galvani theorized that the energy came from the leg itself, but his fellow scientist, Alessandro Volta, believed otherwise.

Volta hypothesized that the frog’s leg impulses were actually caused by different metals soaked in a liquid.

He repeated the experiment using cloth soakedin brine instead of a frog corpse, which resulted in a similar voltage. Volta published his findings in 1791 and later created the first battery, the voltaic pile, in 1800.

The invention of the modern battery is often attributed to Alessandro Volta. It actually started with a surprising accident involving the dissection of a frog.