Daily updates 9 april 2018

National News

1. India and Nepal Agree to Strengthen Bilateral Relations in Key Areas

i. India and Nepal have agreed to further strengthen bilateral relations in key areas of border security, connectivity, trade and agriculture. The two countries agreed to
develop inland waterways for overall economic development of the region.
ii. Aiming to expand cross-border rail linkages, the two sides have also decided to construct a new electrified rail line, with India’s financial support. The rail line will connect the border city of Raxaul in India to Kathmandu in Nepal. 

Static/Current Takeaways Important for NABARD Grade-A Exam 2018-

Nepal Capital- Kathmandu, Currency- Nepalese rupee, President- Bidhya Devi Bhandari, Prime Minister- Khadga Prasad Oli. 

2. Tripura CM Launches State Component of PMKVY

i. Tripura Chief Minister Biplab Kumar Deb launched the state component of Pradhanmantri Kaushal Vikas Yojna (PMKVY) in Agartala. He assured that the target to give training to more than 1 lakh 16,000 youths by 2020.
ii. Tripura is the first state in the North East to implement the state component of PMKVY through Directorate of Skill Development (DSD). 

Static/Current Takeaways Important for NABARD Grade-A Exam 2018-

Tripura CM- Biplab Kumar Deb, Governor- Tathagata Roy, Capital- Agartala.

3. Pradhan Mantri Ujjwala Yojana Launched in Delhi

i. Union Minister Dharmendra Pradhan launched Pradhan Mantri Ujjwala Yojana (PMUY) scheme in Delhi and distributed new LPG connections and cylinders to beneficiaries.
ii. During the event, about 400 LPG connections were handed over to families belonging to below poverty line category. Target under this scheme has been increased from the existing 5 crore connections to 8 crore connections by 2020.

Static/Current Takeaways Important for NABARD Grade-A Exam 2018-

PMUY was launched in May 2016.

The objective of this scheme is to provide deposit-free LPG connections with monetary assistance to women from below poverty line (BPL) households



4. Assam's Spring Festival Begins in Manas National Park

i. The two-day Assam Spring Festival began at the Manas National Park where visitors will get to experience the state's local food, music, handloom and handicrafts. 
ii. The aim of the event is to promote the local food and culture of the fringe villagers. It is an attempt to create a model of alternative livelihood through food, handloom and Cultural Park.

Static/Current Takeaways Important for NABARD Grade-A Exam 2018-

Manas National Park is also a tiger and rhino reserve which covers five districts of Assam.

International News

5. President 3-Nation Visit: India and Equatorial Guinea Sign 4 Agreements

i. India and Equatorial Guinea sign four agreements in the field of agriculture, mining, health, telecommunications and IT after delegation-level talks between Indian President Ram Nath Kovind and Equatorial Guinea President Teodoro Obiang Nguema Mbasogo at Malabo, Equatorial Guinea.
ii. The two countries agreed to work together at UN, where Equatorial Guinea has just begun a two-year term on the Security Council. President Kovind is on the first leg of his 3-nation visit to Equatorial Guinea.

Static/Current Takeaways Important for NABARD Grade-A Exam 2018-

Capital- Malabo, Currency- Central African CFA franc.

6. Nitin Gadkari on 4-Day Visit to South Korea

i. Road Transport and Highways Minister Nitin Gadkari is on a four-day official visit to South Korea. 
ii. Mr Gadkari’s visit is aimed at strengthening ties between the two nations and further cementing cooperation in areas, including sharing of technology, experience in port development and joint participation in port-related construction.

Static/Current Takeaways Important for NABARD Grade-A Exam 2018-

South Korean President- Moon Jae-in, Capital- Seoul.

7. UAE and Malaysia Conclude Joint Military Exercise 'Desert Tiger 5'

i. The United Arab Emirates (UAE) and Malaysia concluded joint military exercise “Desert Tiger 5” aimed at sharing expertise and enhancing joint military actions in Dubai, UAE.
ii. The military exercise was aimed at raising the level of performance and combat efficiency and working together between both countries based on the strategy to improve the overall ability and combat readiness of ground forces.

Static/Current Takeaways Important for NABARD Grade-A Exam 2018-

The UAE Capital- Abu Dhabi, Currency- UAE dirham.

Malaysia Capital- Kuala Lumpur, Currency- Malaysian ringgit.

Banking/Economy News

8. FPI Investment Limit in Government Securities Hiked

i. In a move that could temporarily soften bond yields, the Reserve Bank of India, in consultation with the Government, hiked the foreign portfolio investors (FPI) investment limit in Central government securities (G-Sec) from 5% of outstanding stock now to 5.5% in FY2019 and 6% in FY2020.
ii. The FPI investment in state development loans (SDLs) has been left unchanged at 2% of outstanding stock of securities.

9. Deutsche Bank Names Christian Sewing New CEO

i. Deutsche Bank AG named Christian Sewing as the Chief Executive officer of the Bank. He has replaced John Cryan. Sewing will take over with immediate effect.
ii. Garth Ritchie was promoted to sole head of the securities unit and will become a deputy CEO, along with chief administrative officer Karl von Rohr.

Static/Current Takeaways Important for NABARD Grade-A Exam 2018-

Deutsche Bank established its first branch in India in 1980.

Deutsche Bank Headquarters in Frankfurt, Germany.



10. RBI Switches Back to GDP Scale to Measure Economy

i. The Reserve Bank of India switched back to the gross domestic product (GDP)-based measure to offer its growth estimates from the gross value added (GVA) methodology, citing global best practices.
ii. The government had started analysing growth estimates using GVA methodology from January 2015 and had also changed the base year to 2018 from January.

Static/Current Takeaways Important for NABARD Grade-A Exam 2018-

Urjit Patel- 24th Governor of RBI, Headquarters- Mumbai, Established on- 1st April 1935, in Kolkata.

While GVA gives a picture of the state of economic activity from the producers’ side or supply side, the GDP model gives the picture from the consumers’ side or demand perspective.



11. India's Foreign Exchange Reserves Hit a Life-Time High

i. India’s foreign exchange reserves hit a life-time high of 424.361 billion US dollar after rising by 1.828 billion dollar in the week to March 30, according to the Reserve Bank of India data.
ii. Gold reserves remained unchanged at 21.614 billion US dollar.

Static/Current Takeaways Important for NABARD Grade-A Exam 2018-

Arun Jaitley is the present Finance Minister of India.

Dr Urjit Patel is the 24th Governor of RBI.





RBI Headquarters in Mumbai.

Awards

12. Anushka Sharma to Get Dadasaheb Phalke Excellence Award

i. Bollywood actor Anushka Sharma will be awarded the Dadasaheb Phalke Excellence Award for her successful movies as a producer.
ii. The award will be given by an organisation called Dadasaheb Phalke Foundation, a Mumbai-based organisation, which is different from the Government of India instituted Dadasaheb Phalke Award, awarded during National Awards ceremony held annually in New Delhi.

Sports News

13. Sebastian Vettel Wins Bahrain Grand Prix

i. Ferrari's Sebastian Vettel won his second Grand Prix in as many races, at the Bahrain Grand Prix, while Mercedes' Valtteri Bottas finished second by just 0.699 seconds.
ii. Meanwhile, reigning world champion Mercedes' Lewis Hamilton finished third.

Static/Current Takeaways Important for NABARD Grade-A Exam 2018-

Bahrain Capital- Manama, Currency- Bahraini dinar.

CWG 2018

14. Jitu Rai and Mehuli Ghosh Breaks CWG Record

i. Jitu Rai broke the games record to claim the gold medal by some distance in men's 10m air pistol, at the ongoing 21st Commonwealth Games. Om Prakash Mitharval bagged bronze in the same event. Australia's Kerry Bell secured the silver medal, having managed to topple Mitharval from the second position.
ii. India's 17-year-old shooter Mehuli Ghosh set a Commonwealth Games joint record to win silver in the women's 10m Air Rifle event. Ghosh and eventual gold medallist Singapore's Martina Lindsay Veloso both ended with record score following which the winner was decided by a shoot-off. India's 25-year-old shooter Apurvi Chandela won a bronze medal in the same event.

15. India Win Badminton Team Gold for 1st Time in CWG History

i. India clinched their first-ever badminton mixed team event gold in Commonwealth Games history after defeating defending champions Malaysia 3-1 in the final at Gold Coast.
ii. India's previous best performance in mixed team event at CWG was a silver-medal finish in the 2010 edition. Saina Nehwal and Kidambi Srikanth represented India in singles' matches of the five-member team event.

16. Indian Men's TT Team Wins Gold

i. India defeated Nigeria to clinch gold in the men's table tennis team event at the Commonwealth Games for the first time since 2006.
ii. With this, India joined England to bag second-most table tennis gold medals (5) at CWG. This is the first time that India have won both men's and women's TT team events at a single CWG edition.

17. Weightlifter Punam Yadav Wins 5th Gold For India

i. India’s weightlifter Punam Yadav won gold in the Women’s 69kg weightlifting category. Yadav lifted a combined total of 222kg (100 snatch and 122 clean and jerk) and defeated England’s Sarah Davies her closest competitor to take her second medal at the Commonwealth Games.
ii. This was India’s fifth gold medal in the ongoing games. Venkat Rahul Ragala
earned India the fourth Gold medal after lifting 338 kilograms in the Men’s 85 kg category.

18. Indian Women’s TT Team Wins Gold

i. India has bagged three more Gold, one Silver and two bronze medals at the 21st Commonwealth Games in Gold Coast on the fourth day. Indian women’s Table Tennis team won their first ever Gold Medal defeating Singapore.
ii.  Manika Batra led Table tennis team’s victory was historic as Singapore had never lost since 2002.

Zener diode full explanation

Zener diode

A normal p-n junction diode allows electric current only in forward biased condition. When forward biased voltage is applied to the p-n junction diode, it allows large amount of electric current and blocks only a small amount of electric current. Hence, a forward biased p-n junction diode offer only a small resistance to the electric current.

When reverse biased voltage is applied to the p-n junction diode, it blocks large amount of electric current and allows only a small amount of electric current. Hence, a reverse biased p-n junction diode offer large resistance to the electric current.

If reverse biased voltage applied to the p-n junction diode is highly increased, a sudden rise in current occurs. At this point, a small increase in voltage will rapidly increases the electric current. This sudden rise in electric current causes a junction breakdown called zener or avalanche breakdown. The voltage at which zener breakdown occurs is called zener voltage and the sudden increase in current is called zener current.

A normal p-n junction diode does not operate in breakdown region because the excess current permanently damages the diode. Normal p-n junction diodes are not designed to operate in reverse breakdown region. Therefore, a normal p-n junction diode does not operate in reverse breakdown region.

What is zener diode?

A zener diode is a special type of device designed to operate in the zener breakdown region. Zener diodes acts like normal p-n junction diodes under forward biased condition. When forward biased voltage is applied to the zener diode it allows  large amount of electric current and blocks only a small amount of electric current.

Zener diode is heavily doped than the normal p-n junction diode. Hence, it has very thin depletion region. Therefore, zener diodes allow more electric current than the normal p-n junction diodes.

Zener diode allows electric current in forward direction like a normal diode but also allows electric current in the reverse direction if the applied reverse voltage is greater than the zener voltage. Zener diode is always connected in reverse direction because it is specifically designed to work in reverse direction.

Zener diode definition

A zener diode is a p-n junction semiconductor device designed to operate in the reverse breakdown region. The breakdown voltage of a zener diode is carefully set by controlling the doping level during manufacture.

The name zener diode was named after the American physicist Clarance Melvin Zener who discovered the zener effect. Zener diodes are the basic building blocks of electronic circuits. They are widely used in all kinds of electronic equipments. Zener diodes are mainly used to protect electronic circuits from over voltage.

Breakdown in zener diode

There are two types of reverse breakdown regions in a zener diode: avalanche breakdown and zener breakdown.

Avalanche breakdown

The avalanche breakdown occurs in both normal diodes and zener diodes at high reverse voltage. When high reverse voltage is applied to the p-n junction diode, thefree electrons (minority carriers) gains large amount ofenergy and accelerated to greater velocities. 

The free electrons moving at high speed will collides with the atoms and knock off more electrons. These electrons are again accelerated and collide with other atoms. Because of this continuous collision with the atoms, a large number of free electrons are generated. As a result, electric current in the diode increases rapidly. This sudden increase in electric current may permanently destroys the normal diode. However, avalanche diodes may not be destroyed because they are carefully designed to operate in avalanche breakdown region. Avalanche breakdown occurs in zener diodes with zener voltage (V_z) greater than 6V.

Zener breakdown

The zener breakdown occurs in heavily doped p-n junction diodes because of their narrow depletion region. When reverse biased voltage applied to the diode is increased, the narrow depletion region generates strong electric field. 

When reverse biased voltage applied to the diode reaches close to zener voltage, the electric field in the depletion region is strong enough to pull electrons from their valence band. The valence electrons which gains sufficient energy from the strong electric field of depletion region will breaks bonding with the parent atom. The valance electrons which break bonding with parent atom will become free electrons. This free electrons carry electric current from one place to another place. At zener breakdown region, a small increase in voltage will rapidly increases the electric current. 

• Zener breakdown occurs at low reverse voltage whereas avalanche breakdown occurs at high reverse voltage.
• Zener breakdown occurs in zener diodes because they have very thin depletion region. 
• Breakdown region is the normal operating region for a zener diode.
• Zener breakdown occurs in zener diodes with zener voltage (V_z) less than 6V.

Symbol of zener diode

The symbol of zener diode is shown in below figure. Zener diode consists of two terminals: cathode and anode. 

In zener diode, electric current flows from both anode to cathode and cathode to anode.

The symbol of zener diode is similar to the normal p-n junction diode, but with bend edges on the vertical bar.

VI characteristics of zener diode

The VI characteristics of a zener diode is shown in the below figure. When forward biased voltage is applied to the zener diode, it works like a normal diode. However, when reverse biased voltage is applied to the zener diode, it works in different manner.

When reverse biased voltage is applied to a zener diode, it allows only a small amount of leakage current until the voltage is less than zener voltage. When reverse biased voltage applied to the zener diode reaches zener voltage, it starts allowing large amount of electric current. At this point, a small increase in reverse voltage will rapidly increases the electric current. Because of this sudden rise in electric current, breakdown occurs called zener breakdown. However, zener diode exhibits a controlled breakdown that does damage the device.

The zener breakdown voltage of the zener diode is depends on the amount of doping applied. If the diode is heavily doped, zener breakdown occurs at low reverse voltages. On the other hand, if the diode is lightly doped, the zener breakdown occurs at high reverse voltages. Zener diodes are available with zener voltages in the range of 1.8V to 400V.

Advantages of zener diode

• Power dissipation capacity is very high
• High accuracy
• Small size
• Low cost

Applications of zener diode

• It is normally used as voltage reference
• Zener diodes are used in voltage stabilizers or shunt regulators.
• Zener diodes are used in switching operations
• Zener diodes are used in clipping and clamping circuits.
• Zener diodes are used in various protection circuits

Tunnel diode full explanation

Tunnel diode

Tunnel diode definition

A Tunnel diode is a heavily doped p-n junction diode in which the electric current decreases as the voltage increases.

In tunnel diode, electric current is caused by “Tunneling”. The tunnel diode is used as a very fast switching device in computers. It is also used in high-frequency oscillators and amplifiers.

Symbol of tunnel diode

The circuit symbol of tunnel diode is shown in the below figure. In tunnel diode, the p-type semiconductor act as an anode and the n-type semiconductor act as a cathode. 

We know that a anode is a positively charged electrode which attracts electrons whereas cathode is a negatively charged electrode which emits electrons. In tunnel diode, n-type semiconductor emits or produces electrons so it is referred to as the cathode. On the other hand, p-type semiconductor attracts electrons emitted from the n-type semiconductor so p-type semiconductor is referred to as the anode.

What is a tunnel diode?

Tunnel diodes are one of the most significant solid-state electronic devices which have made their appearance in the last decade. Tunnel diode was invented in 1958 by Leo Esaki.

Leo Esaki observed that if a semiconductor diode is heavily doped with impurities, it will exhibit negative resistance. Negative resistance means the current across the tunnel diode decreases when the voltage increases. In 1973 Leo Esaki received the Nobel Prize in physics for discovering the electron tunneling effect used in these diodes.

A tunnel diode is also known as Esaki diode which is named after Leo Esaki for his work on the tunneling effect. The operation of tunnel diode depends on the quantum mechanics principle known as “Tunneling”. In electronics, tunneling means a direct flow of electrons across the small depletion region from n-side conduction band into the p-side valence band. 

The germanium material is commonly used to make the tunnel diodes. They are also made from other types of materials such as gallium arsenide, gallium antimonide, and silicon.

Width of the depletion region in tunnel diode

The depletion region is a region in a p-n junction diode where mobile charge carriers (free electrons and holes) are absent. Depletion region acts like a barrier that opposes the flow of electrons from the n-type semiconductor and holes from the p-type semiconductor.

The width of a depletion region depends on the number of impurities added. Impurities are the atoms introduced into the p-type and n-type semiconductor to increase electrical conductivity.

If a small number of impurities are added to the p-n junction diode (p-type and n-type semiconductor), a wide depletion region is formed. On the other hand, if large number of impurities are added to the p-n junction diode, a narrow depletion region is formed. 

In tunnel diode, the p-type and n-type semiconductor is heavily doped which means a large number of impurities are introduced into the p-type and n-type semiconductor. This heavy doping process produces an extremely narrow depletion region. The concentration of impurities in tunnel diode is 1000 times greater than the normal p-n junction diode.

In normal p-n junction diode, the depletion width is large as compared to the tunnel diode. This wide depletion layer or depletion region in normal diode opposes the flow of current. Hence, depletion layer acts as a barrier. To overcome this barrier, we need to apply sufficient voltage. When sufficient voltage is applied, electric current starts flowing through the normal p-n junction diode.

Unlike the normal p-n junction diode, the width of a depletion layer in tunnel diode is extremely narrow. So applying a small voltage is enough to produce electric current in tunnel diode.

Tunnel diodes are capable of remaining stable for a long duration of time than the ordinary p-n junction diodes. They are also capable of high-speed operations. 

Concept of tunneling

The depletion region or depletion layer in a p-n junction diode is made up of positive ions and negative ions. Because of these positive and negative ions, there exists a built-in-potential or electric field in the depletion region. This electric field in the depletion region exerts electric force in a direction opposite to that of the external electric field (voltage).

Another thing we need to remember is that the valence band and conduction band energy levels in the n-type semiconductor are slightly lower than the valence band and conduction band energy levels in the p-type semiconductor. This difference in energy levels is due to the differences in the energy levels of the dopant atoms (donor or acceptor atoms) used to form the n-type and p-type semiconductor.

Electric current in ordinary p-n junction diode

When a forward bias voltage is applied to the ordinary p-n junction diode, the width of depletion region decreases and at the same time the barrier height also decreases. However, the electrons in the n-type semiconductor cannot penetrate through the depletion layer because the built-in voltage of depletion layer opposes the flow of electrons.

If the applied voltage is greater than the built-in voltage of depletion layer, the electrons from n-side overcomes the opposing force from depletion layer and then enters into p-side. In simple words, the electrons can pass over the barrier (depletion layer) if the energy of the electrons is greater than the barrier height or barrier potential.

Therefore, an ordinary p-n junction diode produces electric current only if the applied voltage is greater than the built-in voltage of the depletion region.

Electric current in tunnel diode

In tunnel diode, the valence band and conduction band energy levels in the n-type semiconductor are lower than the valence band and conduction band energy levels in the p-type semiconductor. Unlike the ordinary p-n junction diode, the difference in energy levels is very high in tunnel diode. Because of this high difference in energy levels, the conduction band of the n-type material overlaps with the valence band of the p-type material. 

Quantum mechanics says that the electrons will directly penetrate through the depletion layer or barrier if the depletion width is very small. 

The depletion layer of tunnel diode is very small. It is in nanometers. So the electrons can directly tunnel across the small depletion region from n-side conduction band into the p-side valence band.

In ordinary diodes, current is produced when the applied voltage is greater than the built-in voltage of the depletion region. But in tunnel diodes, a small voltage which is less than the built-in voltage of depletion region is enough to produce electric current.

In tunnel diodes, the electrons need not overcome the opposing force from the depletion layer to produce electric current. The electrons can directly tunnel from the conduction band of n-region into the valence band of p-region. Thus, electric current is produced in tunnel diode.

How tunnel diode works?

Step 1: Unbiased tunnel diode

When no voltage is applied to the tunnel diode, it is said to be an unbiased tunnel diode. In tunnel diode, the conduction band of the n-type material overlaps with the valence band of the p-type material because of the heavy doping.

Because of this overlapping, the conduction band electrons at n-side and valence band holes at p-side are nearly at the same energy level. So when the temperature increases, some electrons tunnel from the conduction band of n-region to the valence band of p-region. In a similar way, holes tunnel from the valence band of p-region to the conduction band of n-region.

However, the net current flow will be zero because an equal number of charge carriers (free electrons and holes) flow in opposite directions.

Step 2: Small voltage applied to the tunnel diode

When a small voltage is applied to the tunnel diode which is less than the built-in voltage of the depletion layer, no forward current flows through the junction.

However, a small number of electrons in the conduction band of the n-region will tunnel to the empty states of the valence band in p-region. This will create a small forward bias tunnel current. Thus, tunnel current starts flowing with a small application of voltage.

Step 3: Applied voltage is slightly increased

When the voltage applied to the tunnel diode is slightly increased, a large number of free electrons at n-side and holes at p-side are generated. Because of the increase in voltage, the overlapping of the conduction band and valence band is increased.

In simple words, the energy level of an n-side conduction band becomes exactly equal to the energy level of a p-side valence band. As a result, maximum tunnel current flows.

Step 4: Applied voltage is further increased

If the applied voltage is further increased, a slight misalign of the conduction band and valence band takes place. 

Since the conduction band of the n-type material and the valence band of the p-type material sill overlap. The electrons tunnel from the conduction band of n-region to the valence band of p-region and cause a small current flow. Thus, the tunneling current starts decreasing.

Step 5: Applied voltage is largely increased

If the applied voltage is largely increased, the tunneling current drops to zero. At this point, the conduction band and valence band no longer overlap and the tunnel diode operates in the same manner as a normal p-n junction diode.

If this applied voltage is greater than the built-in potential of the depletion layer, the regular forward current starts flowing through the tunnel diode.

The portion of the curve in which current decreases as the voltage increases is the negative resistance region of the tunnel diode. The negative resistance region is the most important and most widely used characteristic of the tunnel diode.

A tunnel diode operating in the negative resistance region can be used as an amplifier or an oscillator.

Advantages of tunnel diodes

• Long life
• High-speed operation
• Low noise
• Low power consumption

Disadvantages of tunnel diodes

• Tunnel diodes cannot be fabricated in large numbers
• Being a two terminal device, the input and output are not isolated from one another.

Applications of tunnel diodes

• Tunnel diodes are used as logic memory storage devices.
• Tunnel diodes are used in relaxation oscillator circuits.
• Tunnel diode is used as an ultra high-speed switch.
• Tunnel diodes are used in FM receivers