Month: December 2019

  • Properties Of Electromagnetic Waves & Behavior Of Light Waves

    Properties Of Electromagnetic Waves & Behavior Of Light Waves

    In this blog post, we will look at the properties of electromagnetic waves. Then, we will look at the behavior of light waves, which are electromagnetic waves too.

    From X-rays to radio waves to visible spectrum, electromagnetic waves are everywhere around us. Understanding their properties and behavior has helped humanity develop some incredible devices. Without these devices, our daily lives would be impossible.

    In this blog post, we look at some of these useful devices as well as some natural phenomena. We will do our best to help you understand the basics behind them. First, we will look at some of the properties of electromagnetic waves.

    Properties of electromagnetic waves

    1. Wavelength – The length of the wave,i.e., the distance between two consecutive maximum or minimum values of the wave.
    2. Frequency – The frequency is the number of waves (of one wavelength) that pass through a fixed point in unit time (one second).
    3. Amplitude – The maximum displacement of a particle from its original position.
    4. Phase – A particular point on the wave, designated as an angle between 0° and 360°. Phase difference is the displacement of one wave in comparison to another with the same frequency.
    5. Energy – The energy a wave carries is directly proportional to the square of its amplitude. The energy is also directly proportional to the frequency and inversely proportional to its wavelength.
    6. Intensity – Intensity is the amount of light at a particular wavelength.
    7. Color – The wavelength, at which the intensity of a wave is maximum, determines the color of the wave.

    Until now, we looked at the properties of electromagnetic waves. Now we will see how electromagnetic waves behave when they fall on a surface. For easy undersanding, we will consider light waves (from the visible spectrum), which are electromagnetic waves too. So, in the next section, we will look at the behavior of light waves.

    Behavior of light waves

    When electromagnetic waves encounter a new medium or move through a medium, they may exhibit one of the following behaviors. But we won’t look at these behaviors directly. Instead, we will look at some natural phenomena that occur in nature and man-made instruments. Then, we will try to understand the behavior of waves (mostly visible light) associated with that phenomenon.

    How can submarines see what is going on outside water?

    Clue: Due to reflection

    Reflection

    Reflection is the phenomenon due to which, a wave, that hits the interface between two mediums, returns to the same medium from where it hit the interface. In this phenomenon, the angle of incidence and the angle of reflection are always equal.

    Properties of electromagnetic waves - Reflection

    Image credits

    Example

    When you look at a mirror and see your reflection, it is because the mirror reflects the light waves.

    behavior of light waves

    Practical application

    A periscope uses the concept of reflection. Submarines use periscopes to see what is going on above the water while remaining submerged inside water.

    How do a microscope and a telescope differ from a projector?

    Hint: Due to Refraction

    Refraction

    Refraction is the phenomenon due to which, a wave, that hits the interface between two mediums, moves into the other medium with a change of direction, wavelength, and speed.

    Behavior of light waves - Refraction

    Image credits

    Example

    A prism refracts the light wave into different colors. Similarly, water droplets in the atmosphere refract the visible light (coming from the sun) creating a rainbow.

    Properties of electromagnetic waves - A prism refracting white light

    Optical prism refracting a ray of white light.

    Practical application

    Lenses work based on the principle of refraction. A lens refracts the light rays incident upon it. As a result, an image is produced on the other side of the lens, which is larger than the original object. 

    1. A convex lens causes the light rays that come from different parts of a distant object, to converge at a single point (your eye). Therefore, we use it to build objects like telescopes, binoculars, and microscopes.

    Properties of electromagnetic waves - a convex lens

    A convex lens refracting waves – Image credits

    Behavior of light waves - Image enlargement by a microscope

    Image enlargement by a microscope – Image credits

    Behavior of light waves - Image enlargement by a telescope

    Image enlargement by a telescope – Image credits

    2. A concave lens causes the light rays that come from different parts of a distant object, to diverge. Therefore, we use it in objects like projectors to create enlarged images.

    Properties of electromagnetic waves - a concave lens

    A concave lens refracting waves – Image credits

    What makes a beam of light passing through a small hole produce multiple concentric circles on the other side?

    Clue: Due to diffraction

    Diffraction

    When a wave hits an obstacle (or hole), it bends around the obstacle even though it stays in the same medium.  

    Example

    When a red laser beam passes through a circular hole, the resulting wave looks as shown in the picture below.

    Properties of electromagnetic waves - A circular hole diffracting red laser light

    By Wisky – Own work, CC BY-SA 3.0, Link

    Practical application

    The principle of diffraction makes the construction of spectrometers possible. We use spectrometers to study the composition of stars as well as the composition of atoms and molecules.

    When you talk to a person wearing glasses, why can you (sometimes) not see your reflection on it?

    Clue: Due to interference

    Interference

    Interference is the phenomenon that happens when two waves come in contact with each other. Depending on the difference in their phases (time), the resulting wave might have a higher amplitude (constructive) or a lower amplitude (destructive). When a diffracted wave meets the original wave or another diffracted wave, it undergoes interference. Thus, Diffraction is often accompanied by interference.

    Behavior of light waves - A graphical illustration of interference

    Image credits

    Example

    One typical example of interference is the multiple colors you see on a soap bubble.

    Properties of electromagnetic waves - Color patterns on a soap bubble

    By Brocken Inaglory – Own work, CC BY-SA 3.0, Link

    Some of the light waves that fall on the soap bubble get reflected by the upper layer (air-bubble interface). But some of the light waves are transmitted through the soap bubble. Then, a part of these light waves is reflected by the lower layer (bubble-air interface). These light waves reflected by two layers interfere with each other. Consequently, they cancel out some colors while brightening the others.

    Application

    Interference makes the creation anti-reflection coatings for lenses (used in sunglasses, telescopes, microscopes, solar panels, etc.) possible. By adjusting the thickness of the coating, some or all the wavelengths of light waves can be canceled out. This destructive interference prevents any reflection from happening. Anti-reflection coatings have two uses:

    1. Improve appearance by reducing reflection – useful in designing glasses. If you wear a spectacles with an anti-reflection coating, your friend needn’t look at his reflection while talking to you.

    Comparison of spectacles with and without anti-reflection coating

    Without vs With Antireflection coating – Image license

    2. Improve efficiency by reducing reflection and improving transmission – useful in solar panels. Solar panels are covered with glass that improves transmission. As a result, more solar light reaches the solar cells. Hence, more electricity is generated.

    What causes the glare that you see on the highway and the surface of a water-body?

    Clue: Due to polarization

    Polarization

    Polarization is a characteristic unique to transverse waves. In transverse waves, the direction of movement of particles is perpendicular to the direction of movement of the waves. If the direction of the motion of the waves is the X-axis, then these particles can move in any direction along the YZ plane.

    In a linearly polarized wave, the particles oscillate only in a fixed direction (fixed angle along the YZ plane). On the other hand, in an unpolarized wave, they oscillate in all directions (along the YZ plane). However, most sources of electromagnetic waves produce only unpolarized waves, consisting of waves with different polarizations. Therefore, a polarization filter is used to get linearly polarized waves from unpolarized waves.

    A linear polarizing filter at work

    Vertical linear polarization of an unpolarized wave – Image credits

    Example

    The glare you see on the highway while driving, and on a water-body on a sunny day are due to polarization. 

    The light produced by the sun, as well as most artificial light sources, is unpolarized. But the water-body and the highway act as horizontal linear polarization filters naturally, reflecting only the light waves parallel (horizontal) to the surface. When this light enters our eyes, it creates a powerful glare. As a result, it becomes difficult to see clearly under the surface of the water and on a highway.

    Application

    Polarized Sunglasses act as vertical polarization filters. So, they block the harmful glare, which consists of light waves of horizontal polarization. Thus, a person wearing a polarized sunglass can see clearly under the surface of the water and also on a highway.

    An example of polarization

    Image credits

    How to find out if your sunglasses are polarized?

    While wearing your sunglass, slowly tilt your head while looking at a reflective surface. Your head must be perpendicular (at 90°) to your body. Now, if your sunglasses are polarized, the glare should brighten.

    Why can you see through a glass door, but not a wooden door?

    Clue: Due to absorption

    Absorption & Attenuation

    When waves pass through a medium (solid, liquid, or gas), they transfer their energy to the molecules in the medium (or the medium absorbs the energy), making the molecules vibrate. This phenomenon is called absorption.

    As a result, as a wave moves through a medium, it steadily loses energy. Since the energy of a wave is proportional to the square of its amplitude, its amplitude falls as well. This steady loss of amplitude or energy of a wave as it travels through a medium is called attenuation.

    Example

    A medium is considered transparent (to that wave) if only a fraction of the wave’s energy is lost as the wave travels through it. On the other hand, it is considered opaque if all the energy of the wave is lost.

    A glass door is transparent to visible light since it absorbs only a part of the energy of the visible light. Hence, you can see through the glass door. However, a wooden door absorbs all the energy of the visible light. Therefore, it is opaque to visible light (but not to some other radiation).

    Application

    Different tissues in our body absorb X-rays to different extents. This concept forms the basis of the functioning of an X-ray machine.

    We hope that this blog post helped you understand the properties of electromagnetic waves and the behavior of light waves. If you liked this blog post, you will like the following blog posts too:

    1. Different types of Waves
    2. 7 types of electromagnetic waves
  • General Knowledge Quiz

    General Knowledge Quiz

    [tqb_quiz id=’2023′]

  • Financial Crises In History That Devastated The World

    Financial Crises In History That Devastated The World

    This blog post will help you find out what the worst financial crises in history are, what started them, and how they affected the world. Most of us are aware of the financial crisis of 2008 and the global economic recession (large-scale job cuts, a decline in the wealth and assets of people) that followed. Even though a decade has already passed, the world has still not recovered from it.

    A financial crisis can cripple a country by destroying it from the inside. Let’s look at the four most devastating financial crisis that destroyed people’s lives and reduced their lif-time savings to ash.

    Financial crises in history

    A financial crisis is a situation in which the values of assets fall steeply. As the costs of assets decline, fearing further depreciation of these assets, most investors (both people and companies) who invested in these assets try to sell them at the same time, leading to a reduction in demand for these assets.

    Due to the decline in demand, the values of these assets fall further. The investors, who end up selling them, now have a shortage of assets. Due to the loss incurred by selling the assets at lower prices, they have less money to pay their debts.

    When this transforms into a large scale problem, the government intervenes to rescue the financial institutions.

    1. The Great Recession of 2007-2008

    On 15th September 2008, Lehman Brothers, one of the oldest, largest investment banks in the world, filed for bankruptcy. This is considered to be the official start of the financial crisis of 2007-2008.

    Financial crises in history - Picture of a wooden toy house on grass

    How did it happen? – The sequence of events

    1. At the beginning of the 21st century, real estate booms in the US. Investors borrow credit from banks to invest in real estate. Banks provide cheap loans in the hopes that they will get them back.

    2. However, from 2005, due to the rising global energy prices, the (negative) gap between people’s incomes and their debts widens.

    3. Therefore, people are not able to repay their mortgages to the banks.

    4. This leads to a decline in demand for real estate properties. Due to the fall in demand, the values of real estate properties (including those that were mortgaged by people) and other assets held by banks and other financial institutions fall as well.

    5. Many influential banks in the USA and the UK come to the brink of collapse.

    6. The government pumps in billions of dollars to rescue these financial institutions from collapsing.

    7. Meanwhile, in Europe, the sovereign debt crisis takes shape.

    The European sovereign debt crisis – The sequence of events

    8. Due to the financial crisis of 2007-2008 and the economic recession that follows, the banking system of Iceland completely breaks down.

    9. In 2009, this spreads to Spain, Portugal, Greece, Italy, and Ireland.

    10. The other European countries, fearing the collapse of the European Union, agree to bailout (providing vast amounts of money) the affected countries. In exchange, they demand austerity measures like temporarily increasing the tax rate and reducing public spending.

    11. The collapse of the financial system of these countries reduces the FDI (Foreign Direct Investment) in these countries, whereas the adopted austerity measures lead to public turmoil.

    Some of these countries (for example, Greece) still haven’t recovered from this crisis.

    2. The 1998 Asian financial crisis

    In July 1997, a financial crisis began in East and Southeast Asia, which almost caused a worldwide economic meltdown. The crisis began with the collapse of the Thailand currency (Baht).

    Financial crises in history - Picture of a wallet

    How did it happen? – The sequence of events

    1. From 1985 to 1996, Thailand has the highest economic growth rate (9% p.a.) in the world. Its currency, Baht, is pegged (fixed at a specific rate so that it cannot vary) to the US Dollar. This high economic growth rate is mostly due to its exports, and also due to the high interest-rate offered by Thailand’s banks attracting foreign investors to deposit more dollars in Thailand’s banks.

    2. Being optimistic, Thailand borrows heavily to invest in real estate and other projects.

    3. At the same time (beginning of the 1990s), the US is slowly recovering from a recession. To counter the high inflation rates in the country, US banks increase the interest rates. Simultaneously, the cost of the US dollar rises in the global market.

    4. Both these developments in the US affect Thailand adversely. Since the cost of the US dollar has increased in the global market, the prices of Thai products increase as well (since Baht is pegged to the US dollar). Now, Japanese and German products become cheaper to their Thai counterparts.

    5. As a result, exports in Thailand decline sharply. Simultaneously, foreign investors choose to invest in US banks instead of Thailand’s banks due to the increased interest rates in the US.

    6. Left with no other choice, Thailand unpegs the Baht to opt for a floating exchange rate (the value of the currency is no more fixed to the US dollar, it can change) and devalues the Baht (For example, if one dollar was 50 Bahts before, now it will be 70 Bahts).

    7. The intended results are simple: Exports in Thailand will increase. However, imports will become extremely costly. Hence, people will buy domestic products instead of foreign products.

    8. However, due to the steep increase in exports, all wealth flows out of the country. As a result, capital flight (disappearance of wealth) ensues, reducing the purchasing power of Thailand tremendously. This makes several services dependent on imports very costly (for example, some medical surgeries become too expensive because the devices needed become too costly to import).

    9. At the same time, the Thailand government is unable to repay all the foreign debt, because, now, Thailand has to pay more Bahts for the same amount of dollars.

    10. Thus, the Asian financial crisis begins. Within a few years, it spreads to the neighboring Southeast Asian and other Asian countries and eventually to Russia and Brazil.

    11. The IMF (International Monetary Fund) steps in to rescue the sinking economies. It pumps in billions of dollars. In exchange, the borrowing nations are forced to implement austerity measures.

    12. By the end of 1999, the economies of several affected countries have stabilized.

    3. The OPEC Oil Embargo of 1973

    Organization of Petroleum Exporting Countries or OPEC, in short, is a group of 14 countries that are the world’s major oil exporters. The oil crisis began in October 1973, when members of the OPEC issued an oil embargo against the US and other allies of Israel.

    Food for thought:

    What is an embargo?

    An embargo is a penalty (commercial or financial) issued by a country against another country or an individual. An embargo can also prohibit partial/complete trade with that country or group of countries.

    Picture of a petrol bunk

    How did it happen? – The sequence of events

    1. Till 1971, the US followed the Gold standard, and other countries traded in US dollars. However, in 1971, President (of the US) Nixon takes the US off the Gold standard. Hence, countries that hold reserves of American dollars cannot exchange it for gold anymore.

    2. Since the value of the American dollar is not tied to any fixed asset anymore, the value of the American dollar depreciates.

    3. Oil is sold in US dollars. Hence, with the decline in the value of the American dollar, the revenue of OPEC falls as well.

    4. At the same time, the US supports Israel in the war against Egypt.

    5. Both these factors aggravate the OPEC and push it to stop oil exports to the US and other allies of Israel.

    6. In a single year, oil prices quadruple.

    7. Now, people have to spend more money on oil. As a result, they have less money to spend on other goods. At the same time, the prices of common goods increase, leading to inflation, unemployment, and, ultimately, recession.

    8. The oil embargo finally comes to an end in March 1974.

    4. The Great Depression (1929 – 1939)

    The Great Depression is the worst financial crisis of all time. It began on 29th October 1929 with the stock market crash, costing the jobs of 15 million Americans (25% unemployment rate) and reducing the GDP of the world by 15% (During the Wall Street crash of 2007 – 2008, the GDP fell only by 1%).

    Picture of declining stocks

    How did it happen? – The sequence of events

    1. During the 1920s, the economy of the US develops at a fast rate. The wealth of the US doubles during this period, and this period would later come to be known as the ‘Roaring Twenties.’

    2. Even though the prices of most items remain stable, the stock prices soar to the sky, increasing four-fold during this period.

    3. This increase in stock prices encourages people, ranging from prince to pauper, to invest in stocks. Those who don’t have enough money, lend money from banks to invest in stocks.

    4. Since the rise in stock prices is irrational, it instills fear in people’s minds. They start believing that if irrational growth is possible, an irrational decline is also likely.

    5. Since the rise in prices is irrational, the government tries to regulate it by increasing the interests of banks. The government hopes it will encourage people to borrow less and invest less in stocks.

    6. However, this severely affects investments in sectors like construction and automobile, for which people heavily depend on loans from banks. This reduces production (since people buy less, companies start producing less), and people have less work (not necessarily fewer jobs).

    7. At the same time, the prices of stocks fall slightly. Since people had less confidence in stocks, many of them sell their stocks at this point. As a result, the prices of stocks fall further (due to lower demand), and people start selling more, triggering a chain reaction.

    8. Since many people have already lost a lot of money in stocks, they reduce their spending in other areas, probably to preserve wealth for an uncertain future.

    9. Consequently, the production in the US (because demand has reduced) and its wealth start declining steeply by the end of 1929. This ultimately leads to the loss of jobs.

    10. During the Autumn of 1930, people, fearing that banks might close down, demand that their money-deposits be paid in cash. Since most banks only hold a portion of their assets as liquid cash, this leads to banking panics throughout the US. A banking panic arises when a lot of people demand that their deposits in banks be paid in cash, at the same time. As a result, banks try to liquidate most of their loans hastily. This causes several banks to fail.

    11. This continues until 1933. By that time, 20% of the banks that existed in 1931 have already failed.

    12. Due to the Gold standard, the economic downfall of the US also perpetuates to the countries in Europe. The Gold standard is an agreement that many countries signed to make international trade easier. The participating countries fixed the values of their currencies with respect to the cost of gold. As a result, the values of these currencies were fixed against each other.

    Food for thought:

    What are the advantages of Gold standard?

    In the Gold standard, the value of a country’s currency is dependent on the amount of gold it owns. Anyone who has that currency can submit it to the government to get gold equivalent to that value. Since the country can only print as much money as the amount of gold it possesses, it helps prevent inflation and stabilize the economy.

    13. The banking catastrophe ends only in 1933 when President Roosevelt issues a four-day banking holiday. During this time, Congress passes reform legislation. After the holiday, only the banks that are found not to fail are reopened.

    14. He also sets up several organizations to protect the citizens’ deposits in banks and to regulate the stock market.

    15. At the same time, nations around the world (including the US) abandon the gold standard and devalue their currency. This gives them more freedom because they can fix the value of their currencies without worrying about the exchange rates (and gold standard).

    16. As a result, the economies of several nations start recovering slowly. In the US, the economy recovers steadily between 1933 and 1937, and the money supply grows by 42% in this period.

    Recession within the depression – The Recession of 1937 – 1938

    17. Even though the economy has started to grow, the government still has huge budget deficits. So, the government starts reducing government spending and increasing taxes.

    18. At the same time, fearing that an increase in the money supply will cause inflation, the US government implements two new policies.

    Food for thought:

    How can an increase in the money supply lead to inflation in the country? 

    Increased money supply means more money in people’s wallets. More money in people’s wallets means they are willing to pay more to purchase goods. Thus, the prices of consumer goods increase due to an increase in demand, leading to inflation.

    19. The government doubles the reserve requirement ratios (Amount of liquid cash / Total amount of customers’ deposits) for banks and sterilizes all the gold in the system by storing them away in federal reserves and not allowing them to enter into circulation.

    20. These two improvements strongly limit the expansion of money. Very soon, the supply of money starts to decline; people have less money to purchase; production declines; and unemployment increases, leading to another recession in 1937- 1938.

    Recovery

    21. To push the country out of recession, President Roosevelt rolls out a major spending program to increase people’s purchasing power and requests that the Federal Reserve Board reduces its reserve requirements.

    22. As a result, the country starts to come out of recession slowly. However, the economy is still not back to pre-depression levels.

    23. At the same time, the US increases its military spending, due to the fears of the Second world war. This, in turn, increases the government’s budget deficits. To save the economy, the Federal Reserve uses its reserve cash and gold to increase the money supply. This boosts the economy by providing more jobs.

    24. Finally, the second world war brings the Great Depression to an end. Second world war is not the direct reason for the end of the Great Depression. However, the jobs (military, navy, air force, arms production, etc.) it created and the push it gave to the Federal Reserve, to push its cash and gold reserves into the monetary system, ends the Great Depression.

    We hope that you liked this blog post about the worst financial crises in history. If you liked this blog post, also check out the following blog posts:

    1. How to save your money?

    2. Basics of investing

    3. What are cryptocurrencies?

  • Quiz on Waves

    Quiz on Waves

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  • Quiz on the Human Memory

    Quiz on the Human Memory

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  • Quiz on GPS

    Quiz on GPS

    [tqb_quiz id=’1450′]

  • Quiz on Epidemics

    Quiz on Epidemics

    [tqb_quiz id=’1385′]

  • Quiz on the Human Brain

    Quiz on the Human Brain

    [tqb_quiz id=’1364′]