Saturday 18 February 2012

Lightning and Safety

Lightning is caused due to the heavy electric discharge from the clouds to the earth. If lightning is not controlled, it can cause heavy damage to life and property. Hence, protective measures are of utmost importance during lightning strikes. Interiors of buildings are safe places to protect ourselves from lightning strikes. Taking shelter in interiors and not staying in open areas is one of the best measures you can take. You should not take shelter under trees when in the open, or go to an open area if outside. If you are in a vehicle, you should not come out of it; you should also close the doors and windows of the vehicle.

Tall buildings are provided with lightning rods. A lightning rod a metal rod that is erected at the top of a building. It is connected to a thick metallic plate, made of a good conducting material like copper and buried under the earth, through a thick copper wire. If lightning is likely to strike the building, it is attracted by the lightning rod, and the electrical discharge is transferred through the wire to the ground. Thus, it keeps the building safe.

Introduction and Lightning

Lightning is a natural phenomenon that has fascinated people for ages. Several people thought and researched about the cause of lightning and its process. Benjamin Franklin discovered that there is an electric discharge between clouds that produces a spark, and it is the electric spark between the clouds and the earth that appears as lightning. His famous kite experiment proved this fact.
The occurrence of lightning is as follows. The formation of clouds involves friction between water particles in the atmosphere. The friction charges the particles. Among the positive and negative charges, the negative charge accumulates at the bottom of the cloud and the positive charges in its top. As the accumulation of the charge increases, the cloud will create a positive charge on the ground nearby. As the amount of charge increases, the negative charge on the cloud tends to make a path towards the ground, and it results in a narrow streak of electrical discharge, which we call lightning.

An electroscope is a device that detects the type of charge on a body. Like charges repel and unlike charges attract each other. This is used in an electroscope. An electroscope consists of a glass jar fitted with a cork lid and a metallic wire passing through it. There are two metallic strips at the bottom of the wire. The upper end of the wire is connected to a metal disc. A body that is positively charged is touched to the metal disc, so that the charge is transferred to the metal strips through the wire, and they diverge from each other on gaining a like charge. Now, if a negatively charged object is brought into contact with the disc, the strips converge towards each other, indicating the unlike charge on the body. Similarly, if a positively charged body is brought in contact with the metal disc, the divergence of the metal strips increases, indicating the like charge on the body. If the metal disc of the electroscope is touched with the hand, it loses its charge to the ground by transfer of charge through the human body. This is called earthing.

Chemical Effect of Electric Current

The most common application of the chemical effect of electric current is electroplating. In this process, there exists a liquid, usually called the electrolyte, through which current passes. Two electrodes, connected to the terminals of a battery with a switch in between, are inserted in the liquid. The electrode that is connected to the positive terminal of the battery is called the “anode,” and the other connected to the negative terminal is called the “cathode”. Electroplating is done in industries to have an anti-reactive coating on the parts of machines so that they do not react with the raw material, to have an anti-corrosive coating for the machines so that they do not get corroded, and a heat-resistive coating for parts like boilers to resist the heat produced by the machinery.

Gold plating is one of the most common applications of electroplating in ornament-making. In electroplating, the solution gets dissociated into its respective ions. The positive ions are called cations, and the negative ions are called anions. The current in the solution is due to the flow of these ions. The anions move towards the anode, and the cations move towards the cathode. The cationsare converted into atoms at the cathode and form a layer on it, which we call electroplating. To compensate for the loss of ions in the solution, the atoms of the anode dissociate into the solution, forming the ions. The process of electroplating is used for plating parts of vehicles with nickel and chromium, which protects them from corrosion.

Conductivity of Liquids

We can use a tester to check if electricity is flowing through a wire in a circuit. If the bulb in the tester glows, it indicates that current is flowing through the wire; else, current does not exist. Electrical conductivity of liquids can be explained by a simple activity of taking a liquid, like lemon juice, in a container, inserting electrodes in it, connecting the two electrodes to the terminals of a battery with a bulb between them. The bulb glows, indicating that lemon juice is a conductor of electricity. Several liquids can be checked for electrical conductivity on in the same way.

We find that liquids like lemon juice, liquid soap, rain water, salt solution, etc. conduct electricity, whereas liquids like distilled water, oil, etc. do not conduct electricity. The materials that conduct electricity are conductors and those that do not conduct are called insulators. When electricity is passed through a conducting solution, the molecules of the solution dissociate into ions, which cause electrical conduction through the liquid. This process is due to the chemical effect of electric current.

Noise and Music

Any intolerable and irritating sound is called noise. The word noise comes from the Latin word nausea, meaning seasickness.
Music refers to any sound that is pleasant to the ear. Sound produced by musical instruments is pleasing to the ear. But if the intensity of the sound exceeds a certain limit, then it becomes intolerable and is noise.
Undesirable sounds and disturbances cause noise pollution.
Noise pollution may cause high blood pressure, panic attacks and lack of sleep among those exposed to it. To reduce noise pollution, trees should be planted along roads and in residential areas, factories should not be set up in residential areas, vehicles should not blow horns around schools, hospitals and residential area, TVs and music systems should not be played at high volume.
Continuous exposure to loud noise may cause temporary or even permanent hearing impairment.
Sign language is used by the hearing disabled to communicate.

Characteristics of sound

Sound is a form of energy produced by a vibrating body. Sound requires a medium for its propagation. Sound does not propagate in vacuum. Sound is produced due to the vibration of an object.

The to and fro or back and forth motion of an object is called vibration. To produce pleasant sounds, a number of musical instruments have been developed. Some instruments produce sound due to the vibration of membranes, some due to the vibration of strings, and some others produce sound due to the vibration of an air column. The maximum displacement of a vibrating particle from its mean or equilibrium position is called its amplitude. The time taken by the vibrating particle for one full vibration or oscillation is called the time period of vibration. The number of vibrations per second is called the frequency. Frequency is measured hertz (Hz).

Sound produced by any means has the following characteristics, namely, loudness, pitch or shrillness, and quality or timbre.

The loudness of sound depends on its amplitude. The loudness of sound is proportional to the square of the amplitude. A roar of a lion is louder than a woman’s voice. The pitch of sound depends on its frequency. If frequency is more, then the pitch or shrillness is more. The pitch of a woman’s voice is more and it is shriller then a man’s voice. The loudness of sound is measured in Decibel (db). If loudness exceeds 80 db, then the sound becomes physically painful.
Not all sound produced by vibrating bodies is audible. The human ear can only recognise sounds of frequencies in the range of 20 Hz and 20,000 Hz. This range of frequency is called audible sound. Some animals like dogs and snakes can hear sounds of frequencies greater than 20,000 Hz. Sounds of frequencies less than 20 Hz are called infrasonic sounds, while sounds of frequencies greater than 20,000 Hz are called ultrasonic sounds.

Production and Propagation of sound

Sound is a form of energy that causes the sensation of hearing. Sound needs a medium to travel. Sound travels through gases, liquids and solids. The speed of sound is the maximum in solids, less in liquids and the least in gases. Sound cannot travel through vacuum. In humans, sound is produced by the voice box or the Larynx. Vocal cords in the larynx vibrate and produce sound. We hear sound with our ears. The ear drum has a vibrating membrane like a stretched rubber sheet. When a sound note reaches the ear, the ear drum vibrates, and the vibrations get converted into signals that are carried to the brain to get a sensation of hearing.

To produce pleasant sounds, a number of musical instruments have been developed. Some instruments produce sound due to the vibration of membranes, some due to the vibration of strings, and some others produce sound due to the vibration of an air column. The to and fro or back and forth motion of an object is called vibration. The sitar, veena, violin, guitar and ektara are some stringed instruments. The tabla, cymbals, ghatam, kartal and manjira are some instruments that work on the vibration of a membrane, and instruments like the flute and the trumpet produce sound due to the vibration of an air column present in them.