Daily Prelims Notes 19 July 2021

July 19, 2021
Posted by: OptimizeIAS Team
Category: DPN

Daily Prelims Notes

19 July 2021

Table Of Contents

Subject: Science and Technology

Context: One of the worrying aspects of the Pegasus spyware is how it has evolved from its earlier spear-phishing methods using text links or messages to ‘zero-click’ attacks which do not require any action from the phone’s user.

Concept:

A “zero-day exploit” is a completely unknown vulnerability, about which even the software manufacturer is not aware, and there is, thus, no patch or fix available for it. In the specific cases of Apple and WhatsApp, therefore, neither company was aware of the security vulnerability, which was used to exploit the software and take over the device.)

Zero-click attacks working

A zero-click attack helps spyware like Pegasus gain control over a device without human interaction or human error.
So all awareness about how to avoid a phishing attack or which links not to click are pointless if the target is the system itself.
Most of these attacks exploit software which receive data even before it can determine whether what is coming in is trustworthy or not, like an email client.

Google Project Zero security researcher Ian Beer showed how attackers take complete control of an iPhone in radio proximity without any user interaction. The exploit targeted the Apple Wireless Device Link (AWDL), that it was powerful enough to “shut off or reboot systems or to corrupt kernel memory”.

Prevention

Zero-click attacks are hard to detect given their nature and hence even harder to prevent. Detection becomes even harder in encrypted environments where there is no visibility on the data packets being sent or received.
Ensure all operating systems and software are up to date so that they would have the patches for at least vulnerabilities that have been spotted. so, it would not sideload any app and to download only via Google Play or Apple’s App Store.
One way to go is to stop using apps altogether and switch to the browser for checking mails or social media, even on the phone.

Pegasus

All spyware do what the name suggests — they spy on people through their phones.
Pegasus works by sending an exploit link, and if the target user clicks on the link, the malware or the code that allows the surveillance is installed on the user’s phone. (A presumably newer version of the malware does not even require a target user to click a link. More on this below.)
Once Pegasus is installed, the attacker has complete access to the target user’s phone. Pegasus spyware ,the most powerful spyware out there, more potent and almost impossible to detect or stop
The first reports on Pegasus’s spyware operations emerged in 2016, when Ahmed Mansoor, a human rights activist in the UAE, was targeted with an SMS link on his iPhone 6.
The Pegasus tool at that time exploited a software chink in Apple’s iOS to take over the device. Apple responded by pushing out an update to “patch” or fix the issue.
Pegasus delivers “a chain of zero-day exploits to penetrate security features on the phone and installs Pegasus without the user’s knowledge or permission”. Pegasus spyware’s operations were live in 45 countries at the time
Tools such as Pegasus can be used for mass surveillance; it would seem likely that only selected individuals would be targeted.

The key features of Pegasus are:

Ability to access password-protected devices;
Being totally transparent to the target;
Leaving no trace on the device;
Consuming minimal battery, memory and data so as to not arouse suspicion in more alert users;
A self-destruct mechanism in case of risk of exposure; and
Ability to retrieve any file for deeper analysis

2. Loon balloons

Subject: Science and Technology

Context: Florida’s Republican governor, Ron DeSantis, called this week on the administration of President Joe Biden to greenlight a plan to transmit the Internet to people in Cuba via high-altitude balloons when their government has blocked access.

Concept:

What is loon?

Loons are high altitude balloons that provide internet to remote areas. It is the third layer of connectivity ecosystem to help places with minimum reach receives connectivity with the rest of the world. These balloons that reach the stratosphere and provide internet connections to regions that were once thought unservable.

Loon balloons had been providing service in mountainous areas in Kenya through a partnership with a local telecom. The service also helped provide wireless communications in Puerto Rico in the aftermath of Hurricane Maria, which destroyed the island’s mobile network.

How Loon balloons works?

The Loon balloons were effectively cell towers the size of a tennis court. They floated 60,000 to 75,000 feet (18,000- 23,000 meters), above the Earth, well above commercial jetliner routes.
Made of the commonplace plastic polyethylene, the balloons used solar panels for electricity and could deliver service to smartphones in partnership with a local telecom.
Each balloon could serve thousands of people.
But they had to be replaced every five months or so because of the harsh conditions in the stratosphere. And the balloons could be difficult to control. Navigating balloons through the stratosphere has always been hard
Loon had said that beyond the balloons themselves, it needed network integration with a telecom to provide service and some equipment on the ground in the region.
Loon used multiple balloons to extend connections beyond the necessary ground link.

Effectiveness

It would need an unused band of spectrum, or radio frequencies, to transmit a connection to Cuba, and spectrum use is typically controlled by national governments.
Anyone trying this would have to find a free block of spectrum that wouldn’t be interfered.
Balloon- or drone-powered networks aren’t likely to be economical over the long term,
they’re suitable for bridging communications amid disasters or in war zones, the transmission capabilities of such networks isn’t large

3. Messenger RNA vaccines

Subject: Science and Technology

Context: Messenger RNA vaccines against Covid-19 were not detected in human milk, according to a small study by University of California, San Francisco. The paper appears in JAMA Pediatrics.

Concept:

The study analyzed the breast milk of seven women after they received mRNA vaccines from Pfizer or Moderna in the US.
It found no trace of the vaccine, offering the first direct data of vaccine safety during breastfeeding. This early evidence that the vaccine mRNA is not transferred to the infant could allay concerns among those who have declined vaccination or discontinued breastfeeding due to concern that vaccination might alter human milk
The World Health Organization recommends that breastfeeding people be vaccinated
the Academy of Breastfeeding Medicine has said there is little risk of vaccine nanoparticles or mRNA entering breast tissue or being transferred to milk, which theoretically could affect infant immunity.
The authors noted that the study was limited by the small sample size and said that further clinical data from larger populations was needed to better estimate the effect of the vaccines on lactation outcomes.

4. Blue Origin

Subject: Science and Technology

Context: When Blue Origin launches people into space for the first time, founder Jeff Bezos will be on board. No test pilots or flight engineers for Tuesday’s debut flight from West Texas, just Bezos, his brother, an 82-year-old aviation pioneer and a teenage tourist.

Concept:

Blue Origin has completed 15 test flights to space since 2015, carrying up experiments, and Mannequin Skywalker, the company’s passenger stand-in.
The capsules also were recycled.
Blue Origin is expected to open ticket sales soon after Bezos flies.
New Shepard is meant to launch people on brief flights to the edge of space,
The mega New Glenn will be capable of hauling cargo and eventually crew into orbit from Cape Canaveral, Florida, possibly beginning late next year.

New Shephard

It is a rocket system meant to take tourists to space successfully.
The system is built by Blue Origin.
New Shephard has been named after astronaut Alan Shephard, the first American to go to space.
It offers flights to space over 100 km above the Earth and accommodation for payloads.
The system is a fully reusable, vertical take-off and vertical landing space vehicle.

Scientific objectives of the mission:

It is a rocket system that has been designed to take astronauts and research payloads past the Karman line – the internationally recognized boundary of space.

5. Wildfire

Subject: Environment

Context: By nearly every metric, the wildfires in the Western United States are worsening. They are growing larger, spreading faster and reaching higher, scaling mountain elevations that previously were too wet and cool to have supported fires this fierce.

Concept:

Wildfires worsening

In the forests of the Western United States, half of wildfires are initiated by lightning.
Human-caused — frequently started by power lines, cigarettes, cars, camp fires or arson.
In recent years, there’s been an abundance of very dry fuel.
Drought and high heat can kill trees and dry out dead grass, pine needles, and any other material on the bottom of the forest floor that act as kindling when a fire sweeps through a forest.
Wildfire experts see the signature of climate change in the dryness, high heat and longer fire season that have made these fires more extreme.
Forested land in the region burned naturally from lightning or else was intentionally burned by native communities as a form of forest maintenance.

Extreme fire

Wildfires according to metrics including intensity, rate of spread, and severity.
Fire intensity refers to its power, or the energy released from its blaze. Satellites measure the energy and temperature of fires, and research has shown that the power of these blazes has been increasing.
The rate of spread is one of the most important factors, because it suggests that a fire may be less predictable. Though the size, or acreage, of a fire is important, it’s more important to watch how quickly it is moving.
Severity refers to the consequences of a fire, for instance, how many trees are killed. If a fire is tall and burning to the tops of trees and killing them, it could be more challenging to control.

Effects

Like air pollution, wildfire smoke — and particularly the concentration of PM 2.5, or particles smaller than 2.5 microns — can affect the respiratory and cardiovascular systems, For people who are healthy, the smoke can cause a sore throat, coughing, shortness of breath or decreased lung function
. Those already suffering from cardiovascular or respiratory illnesses are at risk of flare-ups and should take extra precautions even when air quality is considered moderate.
the chemical composition of wildfire smoke, which depends on what’s being burned.
Trees and biomass, for instance, will produce a combination of carbon dioxide, methane, and nitrous oxides, whereas burning houses or cars could produce a whole range of compounds, including heavy metals.

Steps recommended

Air quality is particularly bad, stay indoors, keep windows and doors closed and use HEPA filters if possible.
have access to a HEPA filter, there’s evidence that attaching a quality filter to a box fan can be protective. Outdoors wear a form-fitting N95 mask.
Landscaping changes can make a difference, too. Fire experts think in terms of the 0-5 Zone, which refers to the 5-foot perimeter around a house. That zone should be kept clear of debris, firewood, plants or mulch. “

6. Moon Wobble

Subject: Science and Tech

Context: US coastlines will face increasing flooding in the mid-2030s thanks to a regular lunar cycle that will magnify rising sea levels caused by climate change, according to research led by NASA scientists.

A key factor identified by the scientists is a regular “wobble” in the moon’s orbit – first identified in the 18th century – that takes 18.6 years to complete. The moon’s gravitational pull helps drive Earth’s tides.

Concept:

What is moon wobble?

The moon wobble is nothing but a regular swaying in the moon’s orbit. It was first documented way back in 1728. This wobble takes over an 18.6-year period to complete, and continues in a cyclic fashion.
Their results underscored a basic fact separate from the movement of the moon: Our oceans are rising because of climate change.

What impact does this wobble have on Earth?

The moon wobble impacts the gravitational pull of the moon, and therefore, indirectly influences the ebb and flow of tides here on the Earth. In fact, as per the NASA study, each wobble cycle has the power to amplify and suppress the tides on Earth.

One half of the 18.6-year cycle suppresses the tides, which means that the high tides get lower, while the low tides get higher than normal. Once this cycle completes, the situation flips—in the subsequent cycle, the tides are amplified, with high tides getting higher and low tides, lower!

The lunar cycle is expected to shift again by mid-2030, and in the coming phase, the tides will amplify once again.

Moon wobble and climate change: A double whammy situation

The upcoming changes in the lunar cycle will pose a serious threat, as the amplified high tides coupled with the rising sea levels will make the risk of flooding far greater across all coastal regions of the globe.

The study predicts that the high tide-associated floods—also known as nuisance floods or sunny day floods—may occur in clusters that could last for months or even for longer periods!

This surge will be closely associated with the position of the Moon, Earth and the Sun. A NASA statement explains: “When the Moon and Earth line up in specific ways with each other and the Sun, the resulting gravitational pull and the ocean’s corresponding response may leave city-dwellers coping with floods every day or two.”

As per NOAA, episodes of such flooding are already on the rise, especially across the U.S. Atlantic and Gulf coasts. In 2019, over 600 such floods were reported from the US. With these grim projections, the flooding situation is likely to worsen, especially for people living in the low-lying regions of the globe.

Wobble formation

High tides on this planet are caused mostly by the pull of the moon’s gravity on a spinning Earth. On most beaches, you would see two high tides every 24 hours.
The moon also revolves around the Earth about once a month, and that orbit is a little bit tilted. To be more precise, the moon’s orbital plane around the Earth is at an approximate 5-degree incline to the Earth’s orbital plane around the sun.
Because of that, the path of the moon’s orbit seems to fluctuate over time, completing a full cycle sometimes referred to as a nodal cycle — every 18.6 years. It happens on such a slow scale
‘Precession’ is a more specific word than ‘wobble.’ “At certain points along the cycle, the moon’s gravitational pull comes from such an angle that it yanks one of the day’s two high tides a little bit higher, at the expense of the other.
This does not mean that the moon itself is wobbling, nor that its gravity is necessarily pulling at our oceans any more or less than usual.
The emphasis on the nodal cycle is a little bit different from the message we were trying to convey.
High-tide flooding related to climate change is expected to break records with increasing frequency over the next decade, and people who want to accurately forecast that risk have to work with a lot of noisy data, including weather patterns, astronomical events and regional tidal variation.
The moon wobble is part of that noise, but it has always maintained its own slow, steady rhythm.
During its most rapid upward phase, it acts to enhance the effective sea level, and during its most rapid downward phase, like we’re in now, it acts to suppress the effective sea level. It is not part of sea level rise projections because it’s not sea level rise; it’s just an oscillation.

The effect of wobble

The effect of the wobble could cause high tide levels at a beach to oscillate by 1 or 2 inches over the course of its long cycle.
That may sound small. But in certain situations, it can matter quite a bit.
It just kind of raises the baseline and the more your baseline is raised, the smaller weather event you need to cause a flooding event.
Understanding that baseline is important even when we are in the phases of the nodal cycle
It’s important to realize that at the mid-2030s point, where the switch flips and the natural cycle seems to amplify the rate of sea level rise, then we are going to see a rapid change.

7. OPEC+

Subject: International Relations

Context: OPEC+ ministers agreed on Sunday to boost oil supply from August to cool prices which have climbed to 2-1/2 year highs as the global economy recovers from the coronavirus pandemic.

Concept:

OPEC+ last year cut production by a record 10 million barrels per day (bpd) amid a pandemic-induced slump in demand and collapsing prices. It has gradually reinstated some supply to leave it with a reduction of about 5.8 million bp
OPEC+ would adjust its policy if and when Iranian oil returned to the market if the country reached a deal with world powers over its nuclear programme.
Iran is estimated to be able to add some 1.5 million bpd to global supply once the deal is reached and Western sanctions are lifted.
OPEC+ is the alliance of crude producers undertaking corrections in supply in the oil markets since 2017.
OPEC plus countries include Azerbaijan, Bahrain, Brunei, Kazakhstan, Malaysia, Mexico, Oman, Russia, South Sudan and Sudan. (As of 2020, OPEC has a total of 13 Member Countries viz. Iran, Iraq, Kuwait, United Arab Emirates (UAE), Saudi Arabia, Algeria, Libya, Nigeria, Gabon, Equatorial Guinea, Republic of Congo, Angola and Venezuela are members of OPEC.)

8. BSL-3

Subject: Science

Context: India’s Covid-19 vaccination drive is unlikely to get much help from public sector institutions roped in to push up production of the indigenous vaccine, Covaxin. Barring Indian Immunologicals Limited (IIL), the Hyderabad-based subsidiary of the National Dairy Development Board

Concept:

Again building upon the two prior biosafety levels, a BSL-3 laboratory typically includes work on microbes that are either indigenous or exotic, and can cause serious or potentially lethal disease through inhalation. Examples of microbes worked with in a BSL-3 includes; yellow fever, West Nile virus, and the bacteria that causes tuberculosis.
The microbes are so serious that the work is often strictly controlled and registered with the appropriate government agencies. Laboratory personnel are also under medical surveillance and could receive immunizations for microbes they work with.

Common requirements in a BSL-3 laboratory include:

Standard personal protective equipment must be worn, and respirators might be required
Solid-front wraparound gowns, scrub suits or coveralls are often required
All work with microbes must be performed within an appropriate BSC
Access hands-free sink and eyewash are available near the exit
Sustained directional airflow to draw air into the laboratory from clean areas towards potentially contaminated areas (Exhaust air cannot be re-circulated)
A self-closing set of locking doors with access away from general building corridors
Access to a BSL-3 laboratory is restricted and controlled at all times.

9. Inflation

Subject: Economy

Context: While Covid has destroyed our way of life, few predicted how global shutdowns of factories, refineries, and mines could impact prices.

Concept:

Cost-push inflation occurs when overall prices increase (inflation) due to increases in the cost of wages and raw materials. Higher costs of production can decrease the aggregate supply (the amount of total production) in the economy. Since the demand for goods hasn’t changed, the price increases from production are passed onto consumers creating cost-push inflation.

Demand-pull inflation is the upward pressure on prices that follows a shortage in supply, a condition that economists describe as “too many dollars chasing too few goods. ““When demand surpasses supply, higher prices are the result.”

This is demand-pull inflation. A low unemployment rate is unquestionably good in general, but it can cause inflation because more people have more disposable income. Increased government spending is good for the economy, too, but it can lead to scarcity in some goods and inflation will follow.

The main causes of inflation

Monetary Policy: It determines the supply of currency in the market. Excess supply of money leads to inflation. Hence decreasing the value of the currency.
Fiscal Policy: It monitors the borrowing and spending of the economy. Higher borrowings (debt), result in increased taxes and additional currency printing to repay the debt.
Demand-pull Inflation: Increases in prices due to the gap between the demand (higher) and supply (lower).
Cost-push Inflation: Higher prices of goods and services due to increased cost of production.
Exchange Rates: Exposure to foreign markets are based on the dollar value. Fluctuations in the exchange rate have an impact on the rate of inflation.

Benefits from inflation

Inflation being a cause of concern for the economy, doesn’t affect everyone in a bad way. It is a boon for a certain set of people. While consumers lose a part of their purchasing power to inflation, investors gain from it.
Investors investing in assets affected by inflation, if held on for a long time will certainly benefit from it. For example, an increase in housing prices might affect consumers. However, those who have already bought a house will benefit from capital appreciation.

Prevent inflation

To prevent inflation, the primary strategy is to change the monetary policy by adjusting the interest rates. Higher interest rates decrease the demand in the economy. This results in lower economic growth and therefore, lower inflation. Other ways to prevent inflation are:
Controlling the money supply can also help in preventing inflation.
Higher Income Tax rate can reduce the spending, and hence resulting in lesser demand and inflationary pressures.
Introducing policies to increase the efficiency and competitiveness of the economy helps in reducing the long term costs.

The effects of a rise in the inflation rate

A rise in an inflation rate can cause more than a fall in purchase power.
Inflation could lead to economic growth as it can be a sign of rising demand.
Inflation could further lead to an increase in costs due to workers demand to increase wages to meet inflation. This might increase unemployment as companies will have to lay off workers to keep up with the costs.
Domestic products might become less competitive if inflation within the country is higher. It can weaken the currency of the country.

10. China denies politics behind UNESCO move on Barrier Reef

Subject: Environment

Context: A top Chinese official said on Sunday that political tensions between Beijing and Australia were not behind a UNESCO recommendation to place the Great Barrier Reef on its endangered list.

Concept :

About Great Barrier Reef:

It is the world’s most extensive and spectacular coral reef ecosystem composed of over 2,900 individual reefs and 900 islands.
The reef is located in the Coral Sea (North-East Coast), off the coast of Queensland, Australia.
It can be seen from outer space and is the world’s biggest single structure made by living organisms.
This reef structure is composed of and built by billions of tiny organisms, known as coral polyps.
They are made up of genetically identical organisms called polyps, which are tiny, soft-bodied organisms. At their base is a hard, protective limestone skeleton called a calicle, which forms the structure of coral reefs.
These polyps have microscopic algae called zooxanthellae living within their tissues. The corals and algae have a mutualistic (symbiotic) relationship.
It was selected as a World Heritage Site in 1981.

List of World Heritage in Danger

The List of World Heritage in Danger is compiled by UNESCO.
The list is intended to increase international awareness of the threats and to encourage counteractive measures.
Two UNESCO world heritage sites in India that were earlier included in the World Heritage in Danger list but now have been delisted include:

Group of Monuments at Hampi

Manas Wildlife sanctuary, Assam

UNESCO World Heritage Site:

Is a landmark or area which is selected by the UN Educational, Scientific and Cultural Organization (UNESCO)as having cultural, historical, scientific or other form of significance, and is legally protected by international treaties download from collective ray.
It came by Convention Concerning the Protection of the World Cultural and Natural Heritage signed by UNESCO members.
It establish World Heritage Committee comprises of 15 State parties to convention.

Procedure

Every State Party to this Convention shall, in so far as possible, submit to the World Heritage Committee an inventory of property forming part of the cultural and natural heritage, situated in its territory
A country must first list its significant cultural and natural sites; the result is called the Tentative List.
Next, it can place sites selected from that list into a Nomination File.
The Nomination File is evaluated by the International council on monuments and sites and the World Conservation Union.
These bodies then make their recommendations to the World Heritage Committee. The Committee meets once per year to determine whether or not to inscribe each nominated property on the World Heritage List and sometimes defers or refers the decision to request more information from the country which nominated the site.

11. Midday meals leave a long-lasting impact: study

Subject :Govt Schemes

Context: A study on the inter-generational benefits of the midday meal scheme published in Nature Communications.

Concept :

Midday meals scheme:

The scheme guarantees one meal to all children in government and aided schools and madrasas supported under Samagra Shiksha.
It was launched in the year 1995 as the National Programme of Nutritional Support to Primary Education (NP – NSPE). In 2004, the scheme was relaunched as the Mid Day Meal Scheme.
It is a centrally sponsored scheme, hence cost is shared between the centre and the states.

It is implemented using one of the three models:

Decentralized model – Preparing meals on the site by local cooks, Self-help groups etc.
Centralized model – In the place of local on-site cooks, under this model, an external organization cooks food and delivers it to the schools.
International assistance – Various international charity organizations aid government schools.

MDM Rules, 2015

Midday Meal Rules 2015 are notified on 30th September 2015 under National Food Security Act (NFSA) 2013.
Under the MDM rules, schools are empowered to utilize other funds for midday meals in case MDM funds get exhausted.
On occasions where schools and other required bodies are unable to provide cooked meals to children; they are to provide food allowances to beneficiaries.
Accredited labs to take on the monthly testing of meals on a random basis.
Under MDM rules 2015, if children of any school don’t get food for 3 consecutive school days or 5 days in a month, the concerned state government has to fix the responsibility on a person or an agency.

12. Draft Trafficking Rules 2021

Subject : Legislations

Context : The Trafficking in Persons (Prevention, Care and Rehabilitation) Bill, 2021, is likely to be tabled in the ongoing monsoon session of Parliament.

Concept :

Highlights of the Bill:

The bill proposes stringent punishments for offenders, including hefty fines and seizing of their properties.
The Bill also extends beyond the protection of women and children as victims to now include transgenders as well as any person who may be a victim of trafficking.
The draft also does away with the provision that a victim necessarily needs to be transported from one place to another to be defined as a victim.
Exploitation has been defined to include, at a minimum, the exploitation of the prostitution of others or other forms of sexual exploitation including pornography, any act of physical exploitation, forced labour or services, slavery or practices similar to slavery, servitude or forced removal of organs etc.

Applicability:

All citizens inside as well as outside India.
Persons on any ship or aircraft registered in India wherever it may be or carrying Indian citizens wherever they may be.
A foreign national or a stateless person who has his or her residence in India at the time of commission of offence under this Act.
Every offence of trafficking in persons with cross-border implications.
Defence personnel and government servants, doctors and paramedical staff or anyone in a position of authority.

What are the constitutional & legislative provisions related to Trafficking in India?

Trafficking in Human Beings or Persons is prohibited under the Constitution of India under Article 23 (1).
The Immoral Traffic (Prevention) Act, 1956 (ITPA) is the premier legislation for prevention of trafficking for commercial sexual exploitation.
Criminal Law (amendment) Act 2013 has come into force wherein Section 370 of the Indian Penal Code has been substituted with Section 370 and 370A IPC which provide for comprehensive measures to counter the menace of human trafficking.

Trafficking in Persons report 2021:

According to the Trafficking in Persons report 2021, released by the US State Department, the Covid-19 pandemic has resulted in an increase in vulnerability to human trafficking and interrupted existing anti-traffic efforts.
While India did not meet the minimum standards to eliminate trafficking, the government was making significant efforts, although these were inadequate, especially when it came to bonded labour.

13. Double perovskite

Subject: Science and Technology

Context: Scientists at the Indian Institute of Technology, Madras, have crossed a significant milestone in the evolution of the ‘solar perovskite cell’ (SPC) namely, making it both stable and reducing the downsides that come with stability.

Concept:

Electricity is a flow of electrons. As per the classical understanding of the atomic structure, electrons keep orbiting the nucleus of the atom. They have different energy levels.
Even electrons in the same orbit could have varying energy levels. The energy levels are ‘grouped’ into different ‘energy bands’.
The energy band of the electrons that are farthest from the nucleus — valence electrons — is called the ‘valence band’. To get a flow of electrons going, you need to ‘nudge’ the electrons in the valence band to leave the atom.
The electron should be supplied with energy from outside, to raise its energy level to the higher ‘conduction band’. The electron will then move to the next atom. (As electrons jump from atom to atom, their vacant places are immediately taken by other electrons, just as the space vacated by a droplet of water in a river is immediately taken by another water droplet.)
The difference between the valence band and conduction band is called ‘band gap’ and represents the minimum energy required to nudge electrons in the outermost orbits to leave the atom. In a PV cell, the job of ejecting electrons is done by the photons of sunlight.
PV materials that have smaller band gaps convert more solar energy into electricity.

Perovskite

In material science, perovskite refers to a certain arrangement of molecules. Materials whose structure resembles that of calcium titanate (CaTiO3) are called perovskites.
Perovskite is a material that has two positively charged ions (cations) and one negatively charged ion (anion).
The general formula for such material is ABX3
.The solar industry loves perovskites because they milk more electricity out of sunlight than do the conventional crystalline silicon photovoltaic cells.
With the regular PVs it is hard to convert more than 22 per cent of sunlight into electricity; it is generally believed that perovskites can do much better.
A regular crystalline silicon PV cell can go on for over 25 years, perovskites last about a year.
The combination of stability and energy efficiency has been elusive despite long years of effort by scientists the world over.