ELECTRIC CURRENT AND CIRCUITS

IMPORTANT TERMS

Electric Current           Flow of charged particles inside a substance constitutes an electric current.

Conductors                  Materials in which charged particles can move freely are called as conductors. For example - Metals like Copper, Silver, and Gold etc.

Insulators                     Materials in which charged particles cannot move freely are called as insulators. For example - Wood, Rubber etc.

Ions                             Ions are the atoms or group of atoms with a positive or a negative charge.

Anions                          Ions carrying negative charge are called as anions.

Cations                        Ions carrying positive charge are called as cations.

Anode                          The electrode connected to positive terminal of the battery is known as anode.

Cathode                       The electrode connected to negative terminal of the battery is known as cathode.

Electrical Conductivity   The measure of the ability of a substance to allow the electric current to flow is called electrical conductivity of the substance.   

Electrolysis                  The chemical decomposition produced by passing an electric current through a liquid or solution containing ions is known as electrolysis.

Electroplating               The method of coating one metal over another by the using electric current is known as electroplating.

 

Electrical Conductivity of Water

Pure water is a poor conductor, but the water we use in our houses is not pure. It contains lots of impurities which are generally dissolved salts. The presence of impurities makes the water conductive in nature. Tap water, well water and pond water contains impurities and hence conduct electricity. Distilled water is purified water that does not contain impurities so it does not conduct electricity.

We should not touch electrical appliances with wet hands because impure water (due to presence of salts) will allow current to flow and hence we may get electric shock.

Electrical Conductivity of Other Liquids

Most acids and bases dissolved in water are good conductors of electricity. In a set up to check the electrical conductivity of lemon juice and vinegar, the bulb glows, which means both lemon juice and vinegar allow electric current to flow.

Salt solution like sodium chloride (common salt), potassium iodide are good conductors of electricity. Most substance that exist as liquids at room temperature like alcohol, oils etc. are bad conductors of electricity. When substances like salts, acids or bases are dissolved in water, the resultant solutions are fairly good conductors. If the circuit is complete and solution allows electric current to pass through it, then the bulb glows. Due to heating effect of electric current, the filament of the bulb gets heated up to a high temperature and it starts glowing.        

                                    

LED

We can use LED in place of electric bulb in the tester. Advantage of using LED over bulb is that LED even glows at weak current. There are two wires attached to an LED. One is slightly shorter than other. While connecting LED, shorter wire is always connected to negative terminal of the battery and the longer wire is always connected to the positive terminal of the battery.

Magnetic Effect

When we place compass needle close to the wire that is carrying current, it will show deflection due to the magnetic effect of current.

Effect of Impurities on Electrical Conductivity of Water

Electric current requires freely moving charged particles. Moving charged particles are also referred as charge carriers. In metals, these charge carriers are electrons. In liquids, these charge carriers are ions. Ions are the atoms or group of atoms with a positive or a negative charge.

Electrolysis

Pure water is bad conductor of electricity, but when salts dissolve in water, they form ions and these ions make it possible for an electric current to pass through the solution. This solution is known as electrolyte which contains sodium and chlorine ions that conducts electric current.

When electric current is allowed to pass through this salt solution in an arrangement of electrolytic cell containing rods of conducting material, sodium ions gets attracted towards electrode connected to the negative terminal of the battery known as cathode and chloride ions being negatively charged get attracted towards electrode connected to the positive terminal of the battery known as anode. In this process Hydrogen gas is released at cathode and chlorine gas is released at anode.

 

                                         

Use of Electrolysis

1. Electrolysis is used in industry for the production of many metals and non-metals.
2. Electrolysis is commonly used for coating one metal with another. This method of coating one metal over another by the use of electric current is known as electroplating.
3. Electrolysis is also used in electro refining. In this method electric current is used to purify impure metals.

Electroplating

The method of coating one metal over another by use of electric current is known as electroplating.

                                

 

In the process of electroplating the object to be electroplated is used as Cathode and the metal which is used for coating is used as Anode.

Electrolyte is the solution of soluble salt of metal to be deposited. In the diagram above, solution is copper sulphate which decompose in to copper and sulphate ions after passing of electric current through the solution.

Uses of Electroplating

1. Metals which corrode easily are electroplated with metals which do not corrode easily. For example - Nickel and chromium are widely used in industry for this purpose because they do not corrode and are also scratch resistant. They also give shiny appearance to the rough metals.

2.) Electroplating is also used for decorative purpose. For example- cutlery, statues and    jewellery made up of cheaper metals are coated with gold and silver to give them expensive look.

3.) Electroplating is used in manufacture of printed circuit boards, which are used in TV, computers etc.

 

Uses of Electro refining

Electro refining is the process to purify impure metal by the use of electric current.

 

                              

                                                        

In the process of electro refining, an impure copper rod is taken as anode, which means it is connected to the positive terminal of the battery.

A very thin strip of pure copper is taken as cathode, which means it is connected to the negative terminal of the battery.

Electrolyte is the solution of copper sulphate. On passing electric current to the solution, the impure copper dissolves into the solution and the pure copper metal gets deposited at cathode. The impurities that collect below the anode are known as anode mud.

INTERESTING FACTS

• Lightning strike produces Ozone, which produce characteristic smell. Ozone has very sharp smell, similar to chlorine that we can smell after thunderstorm.
• Every hydrogen atom in our body is likely to be 13.5 billion years old, since they were created at the birth of the universe.
• If we pour handful of salt into glass of water, the water level will go down; the volume decreases by 2%.
• Cars airbags are packed with salt sodium azide, which is very toxic but when the collision takes place, the car’s sensors creates electric pulse which raise the temperature of this salt and decompose it into nitrogen gas which is harmless and expands the airbag.
• In 1880’s there was a ‘War of currents’ between Thomas Edison (who invent direct current) and Nikola Tesla (who invent alternating current). They both wanted their invention to be used, but eventually alternating current won because it is safer and can be used over longer distances.