Damages due to lightning flashes are very common. But with the help of a lightning conductor we can save our large buildings on which we have spent lots of money.
The lightening conductor consists of a large no of conductors having sharp pointing heads. They are usually attached on the top of buildings. Their pointing heads are connected to a conducting material such as a copper wire. Then this copper wire of large length came down along the either side of the building. At the bottom it is attached to a metallic plate. Then that metal plate is interred into the ground. Clouds mostly contain positive charge. Whenever the passage of cloud occurs over a certain building then induce charges will produce. At the pointing heads of the conductor induced positive charge will produce and on the metal plate induced negative charge will be produced. The pointing heads of the conductor have the property of discharging the positive charge present on it. Due to discharging of the positive charge from heads, a positively charged wind will be produced. On account of this wind the negative charge of the cloud will be counteract i.e. cancel out. The charge of the cloud after discharging will flow to the ground with the help of the copper wire.
Hence our building will be saved by using this lightning conductor.
Now let’s check the action of the sharp edges of the pointing conductor.
As we know that the surface charge density of a spherical conductor is calculated by the formula.
= Charge / Area ———-2.32
But we have to find the density in case of a pointed conductor. For a pointed conductor the radius r will be small. Radius r and
are inversely proportional to each other. So, the
will be increased by a large amount. The tiny particles of the air which comes in direct contact with the pointing ends, and will get the same charge as that of the heads of the conductor. Due to similar charges repulsion will take place. Due to the above reason an electrically charged wind is produced, which continuously starts moving the charge far from the conductor’s pointing ends. In other words we can say that the act of dispersing/spraying of charge takes place. This phenomenon is called as corona discharge.
So, it is cleared that the spherical conductors having small radii can never be used to store charge. For storing charge radii of the conductors must be large.
