Type: Prelims Only

With the monsoon making a slow revival over several parts of India, except the northwest region, there is a rise in lightning-linked deaths.

What is lightning?

• Lightning is a very rapid — and massive — discharge of electricity in the atmosphere, some of which is directed towards the Earth’s surface.
• These discharges are generated in giant moisture-bearing clouds that are 10-12 km tall.
• The base of these clouds typically lies within 1-2 km of the Earth’s surface, while their top is 12-13 km away.
• Temperatures towards the top of these clouds are in the range of minus 35 to minus 45 degrees Celsius.

How does it strike?

• As water vapour moves upward in the cloud, the falling temperature causes it to condense.
• Heat is generated in the process, which pushes the molecules of water further up.
• As they move to temperatures below zero degrees Celsius, the water droplets change into small ice crystals. They continue to move up, gathering mass — until they are so heavy that they start to fall to Earth.
• This leads to a system in which, simultaneously, smaller ice crystals are moving up and bigger crystals are coming down.
• Collisions follow and trigger the release of electrons — a process that is very similar to the generation of sparks of electricity.
• As the moving free electrons cause more collisions and more electrons, a chain reaction ensues.
• This process results in a situation in which the top layer of the cloud gets positively charged, while the middle layer is negatively charged.

Making of the thunder

• The electrical potential difference between the two layers is huge — of the order of a billion to 10 billion volts.
• In very little time, a massive current, of the order of 100,000 to a million amperes, starts to flow between the layers.
• An enormous amount of heat is produced, and this leads to the heating of the air column between the two layers of the cloud.
• This heat gives the air column a reddish appearance during lightning. As the heated air column expands, it produces shock waves that result in thunder.

How does this current reach the Earth from the cloud?

• While the Earth is a good conductor of electricity, it is electrically neutral.
• However, in comparison to the middle layer of the cloud, it becomes positively charged.
• As a result, about 15%-20% of the current gets directed towards the Earth as well.
• It is this flow of current that results in damage to life and property on Earth.
• There is a greater probability of lightning striking tall objects such as trees, towers or buildings.
• Once it is about 80-100 m from the surface, lightning tends to change course towards these taller objects.
• This happens because air is a poor conductor of electricity, and electrons that are travelling through air seek both a better conductor and the shortest route to the relatively positively charged Earth’s surface.

What precautions should be taken against lightning?

• Lightning rarely hits people directly — but such strikes are almost always fatal.
• People are most commonly struck by what are called “ground currents”.
• The electrical energy, after hitting a large object (such as a tree) on Earth, spreads laterally on the ground for some distance, and people in this area receive electrical shocks.
• It becomes more dangerous if the ground is wet (which it frequently is because of the accompanying rain), or if there is metal or other conducting material on it.
• Water is a conductor, and many people are struck by lightning while standing in flooded paddy fields.
• For the reasons given above, taking shelter under a tree is dangerous. Lying flat on the ground too can increase risks.
• People should move indoors in a storm; however, even indoors, they should avoid touching electrical fittings, wires, metal, and water.

Answer this PYQ in the comment box:

Q.During a thunderstorm, the thunder in the skies is produced by the:

1. meeting of cumulonimbus clouds in the sky
2. lightning that separates the nimbus clouds
3. violent upward movement of air and water particles

Select the correct option using the codes given below (CSP 2011):

(a) 1 only

(b) 2 and 3 only

(c) 1 and 3 only

(d) None of the above

The 2020 Millennium Technology Prize has been awarded to Shankar Balasubramanian and David Klenerman, for their development of revolutionary Next-generation DNA sequencing techniques.

About Millennium Technology Prize

• The Millennium Technology Prize is one of the world’s largest technology prizes.
• It is awarded once every two years by Technology Academy Finland, an independent fund established by Finnish industry and the Finnish state in partnership.

What is next-generation DNA sequencing?

• Next-generation sequencing (NGS) is a massively parallel sequencing technology that offers ultra-high throughput, scalability, and speed.
• The technology is used to determine the order of nucleotides in entire genomes or targeted regions of DNA or RNA.
• These technologies allow for sequencing of DNA and RNA much more quickly and cheaply than the previously used sequencing.
• NGS has revolutionized the biological sciences, allowing labs to perform a wide variety of applications and study biological systems at a level never before possible.
• More than a million base pairs can be sequenced, which translates to hundreds of genes or even the whole genome of an organism.
• This is made possible by simultaneously sequencing hundreds of pieces of DNA at the same time.

What is sequencing, btw?

• DNA (or RNA, in some viruses), the genetic material of life forms, is made of four bases (A, T, G and C; with U replacing T in the case of RNA).
• A chromosome is the duplex of a long linear chain of these – and in the DNA sequence is information – the blueprint of life.
• Life famously can replicate, and DNA replicates when an enzyme, DNA polymerase, synthesises a complementary strand using an existing DNA strand as the template.
• The breakthrough idea of Balasubramanian and Klenerman was to sequence DNA (or RNA) using this process of strand synthesis.
• They cleverly modified their ATGC bases so that each shone with a different colour.
• When copied, the “coloured” copy of DNA could be deciphered from the colours alone, using miniature optical and electronic devices.

What about the cost of all this sequencing?

• When the Human Genome Project delivered the first, near-complete sequence of our genome, the cost was estimated to have been 3 billion dollars.
• As all our chromosomes together have 3 billion base pairs, it becomes an easy calculation – One dollar per sequenced base.
• By the year 2020, NGS technologies has pushed the price for sequencing to a few thousands of rupees.

Back2Basics:

What is the Human Genome Project?