In what atmospheric conditions is dew formed?

Moisture in the atmosphere turns into dew droplets when it comes in contact with any cold substance. Green grass, leaves, metal wires, threads of spider webs etc are substances that collect dew. These substances absorb heat in day-time when the sun is up, and during night they lose the heat and become cool. The condition for dew to form is that the temperature of the substance must reach the dew point. And to allow the temperature to fall thus the atmosphere must be free of clouds. Clouds store heat. So if the atmosphere is cloudy then the heat emitted from clouds would not allow the temperature to fall to the dew point during night, and dew would not form. It is also necessary for formation of dew that relative humidity of air is about 100%.

A thing to note here is that the dew point itself is not a constant like boiling point or melting point. The temperature at which dew is formed is called dew point. Albeit, it would always be greater than 0° Celsius which is the freezing point of water; or else instead of liquid droplets we would see ice crystals for dew.

Additional reading:
Dew (Wikipedia)


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What is the formula to calculate IQ? Is IQ of 100 good?

Intelligence is an abstract concept. It is difficult to measure intelligence level and express it in numbers. However, the term Intelligence Quotient is used for the purpose. This term became popular about a hundred years ago in 1916 when a Stanford University psychologist named Lewis Terman invented a formula to numerically measure the amount of intelligence in a human being. The formula was revised in 1937, then in 1960, and the last time in 1972 there were a few changes done to the formula. The formula used today to measure IQ is as follows:

IQ = Mental Age ÷ Physical Age x 100

In the formula, physical age is one's age from the date of birth, but mental age is a completely different matter. To explain with an example, if a 10-year-old correctly answers questions which can normally only be answered by a 13-year-old, then even though his physical age is 10 years, his mental age is considered to be 13 years. Thus, according to the formula, his IQ would be 13 ÷ 10 x 100 = 130. On the other hand, if a 10-year-old answers questions which can normally only be answered by a 10-year-old (and he can't answer tougher questions), then his IQ would be 10 ÷ 10 x 100 = 100. It means his mental and physical age are the same.

IQ Distribution

A person with IQ of 100 can not be said to have a sharp mind, because the IQ figure of 100 is normal. It also means that majority of the people the in world have an IQ of 100. Refer above the distribution of Intelligence Quotient.

To tell the truth, human intelligence level can not be determined mathematically with accuracy, intelligence being an abstract concept. Therefore, the formula for measuring IQ is not very reliable. According to this formula a woman named Marilyn vos Savant has IQ of 228, whereas Albert Einstein's IQ is said to be 160.


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How does polygraph test work? Is it accurate in detecting lies?

Polygraph is a scientific term for what is popularly known as lie detector. It is an instrument used in criminal investigations to find out if the person being prosecuted is telling the truth. Many employers, too, use lie detectors during job interviews to check veracity of job applicants' answers to the interview questions.

Polygraph test involves attaching multiple (hence the prefix poly) sensors (usually four to six) on a subject's body to measure physiological functions like breathing, pulse rate, blood pressure, perspiration etc while the subject is ran through a series of questions. Some polygraph tests record bodily movements such as movement of hands and legs. These sensors send signals to a computer which records them as a horizontally moving graph (see, picture below). The idea behind polygraph test is this: Lying puts stress on the person lying. And this stress is detected though physiological functions, e.g. increased breathing and pulse rate, high blood pressure, sweating,.. At a point where any of these stress signals is detected in the subject the graph would capture that as a spike.

Polygraph Test

An examiner in a polygraph test starts with very simple questions ("What is your name?", "Do you reside at..?",..) and moves on to slightly stress inducing questions such as those involving personal details. This is necessary to establish the baseline of physiological responses in the subject, because different people experience different level of stress while answering a particular type of question. By running this routine of escalating questioning the examiner would know what is the normal level of stress experienced by the subject being examined, which is then compared with the unusual spikes in the polygraph.

Accuracy of polygraph tests is still a subject of debate as the opinions are widely divided. There are ways in which polygraph can be "fooled". These involve 1) using of drugs while under the test to neutralize emotions, 2) biofeedback training, 3) "nail-in-the-shoe" technique in which the subject would press his foot against a sharp nail hidden in the shoe to cause pain which would skew the polygraph results, etc. Not to mention that polygraph test is completely ineffective on psychopaths (people with inability to feel emotions). Polygraph's accuracy also varies by the type of equipment used and proficiency level and subjectivity of the examiner. When conducted without manipulation on the subject's part, polygraph tests are fairly accurate. According to American Polygraph Association (APA) the accuracy rate of polygraph tests is 80-90%.

Here is a real world example of effectiveness of polygraph test: A private investigator in the US, named Scott Lewis (of Scott Lewis Private Investigation), took a polygraph test to test its accuracy. The test was conducted by Neil Myres who runs the company called Forensic Polygraph Services. Myres asked Lewis to choose a number between 1 to 7, and then he would ask him, one-by-one, whether the number chosen is 1, or 2, or 3, and so on. Lewis was asked to say "no" each time. This means he would be lying to one of the questions. It was a simple test, involving inconsequential questions. Lewis expected to pass the test as he did not think the questions would be stressful. Moreover, he already knew the questions. However, he was surprised by the results of the test. The number he had mentally chosen was 5. He saw on the graph paper that as Myres asked if it was the number 4 the graph showed an upward movement; and it peaked on the fifth question when he was asked if it was the number 5 and Lewis had to lie.

Additional reading:
Polygraph (Wikipedia)

How long is the life of passenger planes like Boeing-747 (Jumbo Jet) and Airbus?

There are three ways of ascertaining the life of an aircraft based on about a dozen factors like its frame construction, weight, engine strength, average flight time, etc. The first unit of measuring longevity of an aircraft is year. A passenger aircraft like Boeing-747 or Airbus 300 is normally considered "aged" after 20 years of service. However, it is inadequate to ascertain the age of an airplane in years alone. It is also important to take into account the number of take-offs and landings by an aircraft within a span of time, which is called usage cycle.

At the time of landing an aircraft endures a mild collision vertically, whereas during take-off the entire frame endures a horizontal pull. Aircraft's metal then "tires" just like human muscles after physical hard work, and gradually becomes weak. To talk in the language of engineering, an aircraft experiences metal fatigue. The most memorable example for this is of Boeing-737 of Aloha Airlines in Hawaii. Flying between various islands this plane took off from the runway for a similar flight on April 1988, and when it was at the height of thousands of feet all of a sudden its roof went off. One air-hostess and a passenger were thrown out with the wind, while the other passengers had their seat-belts on, hence they remained safe with minor injuries. Eventually the plane landed on the airport, but in the below picture you can see the condition it is in. After this accident Boeing declared the life of Boeing-737 to be 75000 cycles. It means once the aircraft completes 75000 take-offs and landings its life is over.

Aloha Airlines' Boeing-737 Accident

The third unit of measuring an aircraft's life is hours of flight. At the latitude of 32000-33000 feet the air temperature is about minus 48° Celsius. Plane's metal is contracted at that low temperature. After beginning to land, within 15 minutes as the plane hits the ground the air temperature is much higher, possibly around 30° Celsius. Such a difference in temperature within 15 minutes is no small matter. As a result of this an aircraft experiences another kind of metal fatigue which diminishes its strength. By this measure, the life of Boeing-737 is 51000 hours of flight. Whereas the life of the supersonic Concord is 45000 hours of flight. For more information about different planes refer to the table below. As shown in the table there are three parameters of longevity. A take-off and landing equals one cycle. Boeing-747 (Jumbo Jet) is meant for International travel, hence it does fewer take-offs and landings and has higher hours of flight compared to the planes used for domestic flights.



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Why are drops of liquid always spherical in shape?

Every molecule of liquid draws its neighboring molecules towards it, and is itself also drawn towards every neighboring molecule. Only the molecules which are on the surface are not drawn externally. Beyond the surface there are no further molecules, hence obviously there is no question of being pulled by other molecules in the outward direction. Result: Every molecule on the surface faces equal pull inward. It is as if the common center in the liquid is exerting equal pull on each of the molecules and drawing them towards it. Thus, liquid naturally takes spherical shape and a droplet is formed. Albeit, not necessarily every droplet is a perfect sphere. The form ultimately depends on the size of a droplet. For example, below picture shows droplets of mercury.


The first one is a perfect sphere because every droplet "tries" to keep the surface area to the minimum. As the drops get bigger they are flattened out. Due to large size the pull between the molecules is not enough to hold them together strongly. The same applies to water droplets as well, which we see sliding on the leaves of plants without wetting the surface.


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What are the causes and treatments of pimples or acne?

Pimples or acne are a combined result of several bodily changes that occur around puberty. During puberty, secretion of the hormone called androgen increases in both boys and girls. Androgen can also increase because of hormonal changes related to pregnancy or starting or stopping birth control pills. It normally happens around teenage and makes the sebaceous (oil) glands become more active. Sebaceous glands are on the hair follicles under the skin. In humans sebaceous glands exist throughout the body except the palms and soles. There is abundance of sebaceous glands on the face. These glands produce sebum, an oily substance which carries dead skin cells through the follicles to the surface of the skin. In normal circumstances sebum is produced in small amount and is discharged through a narrow pore on the skin. But if the quantity of sebum produced is high, it is not discharged as easily. It accumulates under the skin and the part near the pore turns black because of oxidation with the air. This part is generally referred to as blackhead. Blackheads spoil the looks, and it doesn't stop there. After a while bacteria develop in the sebum and that causes inflammation of the skin, worsening the pimple. After the sebum is removed, there remains a permanent dent on that part of the skin.

Formation of Acne

To some extent, genes are found to be responsible for pimples or acne. If one's parents had pimples, once stands greater chances of having pimples. However, upon noticing the first signs of pimple certain precautions can be taken to prevent its growth.

  • It is advisable to wash the face with warm water at regular intervals.
  • Using lotions and creams is not at all advisable as cosmetics that have oily content may clog pores.
  • Excessive chocolate consumption is suggested to aggravate pimples by some researchers. Although this research hasn't found all round support, but chocolate is anyway better avoided.
  • Milk and milk products are also found responsible for pimples.

If pimples or acne increase too much then a lotion containing a form of vitamin A called Retinol or an antibiotic like Tetracycline are advisable. Ultraviolet treatment may also be necessary after consulting a skin specialist.

Additional Reading:
Androgen (Wikipedia)
Sebaceous gland (Wikipedia)
Retinol (Wikipedia)
Tetracycline (Wikipedia)

Why does the ocean appear blue? Is it because of the sky's reflection?

Common sense would suggest that the ocean should appear green, because about two meters below the surface of the ocean the water is filled with organisms and plants containing chlorophyll (a green pigment) which provide about 70% of oxygen quota to the life on Earth. However, the British physicist Lord Rayleigh (who isolated Argon gas in the Earth's atmosphere in the year 1894) investigated this phenomenon and explained that the ocean appears blue because it reflects the color of the sky.

C. V. Raman
Years later in the year 1921, an Indian scientists C.V. Raman (photo, left) was returning via sea route from Britain after attending a physics related session. When he saw blue color of the ocean he remembered the Nobel Prize winner Lord Rayleigh's explanation about it. It then occurred to Raman that if the ocean was indeed reflecting the color of the sky then after filtering the blue color with polarizer we should be able to see the real color of the sea. Subsequently he carried out this experiment, but even after filtering the blue color with polarizer the ocean looked blue. The explanation Raman derived was: Like the sky, the ocean's molecules do not absorb blue light of the sun rays. Red, orange and yellow are absorbed by the water while the color blue is scattered. By scattering we mean the process by which radiation is absorbed and then reradiated by the material through which it passes. This is the same reason why the sky looks blue. For this explanation C.V. Raman was accorded Nobel Prize for physics in the year 1930.

The significance of this discovery was that it gave way to the new science of spectroscopy.

Additional reading:
C. V. Raman (Wikipedia)
Chlorophyll (Wikipedia)
Spectroscopy (Wikipedia)
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