Wednesday, July 29, 2015

List of scientists whose names are used as SI units

Source: Wikipedia

List of scientists whose names are used as SI units is the list of those scientists whose names are assigned as the names of the international units by the International Committee for Weights and Measures. The International System of Units (abbreviated SI from French: Système international d'unités) is the most widely used system of units of measurement. There are seven base units and 22 derived units[1] (excluding compound units). These units are used both in science and in commerce. Two of the base units and 17 of the derived units are named after scientists.[2] By this convention, their names are immortalised. Below is the list of the scientists whose names are used as SI units.

Base unit[Note 1] Derived unit

(colour legend)

Name[3][4] Life Nationality Quantity[5] SI unit[Note 2] Image
André-Marie Ampère[6] 1775–1836 French Electric current [7] ampere (A)
(Base unit)
Ampere Andre 1825.jpg
William Thomson, 1st Baron Kelvin[8] 1824–1907 British (Scottish) Thermodynamic temperature[9] kelvin (K)
(Base unit)
Lord Kelvin photograph.jpg
Blaise Pascal[10] 1623–1662 French Pressure[11] pascal (Pa) Blaise pascal.jpg
Isaac Newton[12] 1643–1727 British (English) Force[13] newton (N) GodfreyKneller-IsaacNewton-1689.jpg
Anders Celsius[14] 1701–1744 Swedish Temperature[15] degree Celsius (°C) Anders Celsius.jpg
Charles-Augustin de Coulomb[16] 1736–1806 French Electric charge[17] coulomb (C) Charles de coulomb.jpg
James Watt[18] 1736–1819 British (Scottish) Power[19] watt (W) Watt James von Breda.jpg
Alessandro Volta [20] 1745–1827 Italian Electric potential[21] volt (V) Volta A.jpg
Georg Simon Ohm[22] 1789–1855 German Electrical resistance[23] ohm (Ω) Ohm3.gif
Michael Faraday[24] 1791–1867 British (English) Capacitance[25] farad (F) Michael Faraday 001.jpg
Joseph Henry[26] 1797–1878 American Inductance[27] henry (H) Joseph Henry (1879).jpg
Wilhelm Eduard Weber[28] 1804–1891 German Magnetic flux[29] weber (Wb) Wilhelm Eduard Weber II.jpg
Ernst Werner von Siemens [30] 1816–1892 German Conductance[31] siemens (S) Ernst Werner von Siemens.jpg
James Prescott Joule[32] 1818–1889 British (English) Energy[33] joule (J) Joule James Jeens engraving.jpg
Antoine Henri Becquerel[34] 1852–1908 French Radioactivity[35] becquerel (Bq) Becquerel Henri photograph.jpg
Nikola Tesla [36] 1856–1943 Serbian[Note 3]-American Magnetic flux density[37] tesla (T) Tesla3.jpg
Heinrich Rudolf Hertz[38] 1857–1894 German Frequency[39] hertz (Hz) Heinrich Rudolf Hertz.jpg
Rolf Maximilian Sievert[40] 1896–1966 Swedish Dose equivalent of radiation[41] sievert (Sv) Rolf Sievert 1896-1966.jpg
Louis Harold Gray [42] 1905–1965 British (English) Absorbed dose of radiation[43] gray (Gy)

Napier and Bell

Napier and decibel are two dimensionless units used to define relative amplitudes in logarithmic scales.[Note 4] They are not SI units, but their usage together with SI units is permitted.

Name Life Nationality Quantity Unit Image
John Napier[44] 1550–1617 British (Scottish) Magnitude (natural logarithmic) [45] neper (Np) John Napier (Neper).jpg
Alexander Graham Bell[46] 1847–1922 British (Scottish)-American Magnitude (common logarithmic)[47] bel (B) Alexander Graham Bell.jpg

See also

Friday, July 24, 2015

21 Golden Electric Safety Rules

Rule no. 1
Avoid contact with energized electrical circuits. Please don’t make fun of this rule if you already know this (and you probably already know if you are reading these lines) and remember that if something bad occurs – you probably won’t have second chance. That’s not funny.

Rule no. 2
Treat all electrical devices as if they are live or energized. You never know.

Rule no. 3
Disconnect the power source before servicing or repairing electrical equipment.
The only way to be sure.

Rule no. 4
Use only tools and equipment with non-conducting handles when working on electrical devices.
Easy to check.

Rule no. 5
Never use metallic pencils or rulers, or wear rings or metal watchbands when working with electrical equipment. This rule is very easy to forget, especially when you are showing some electrical part pointing with metallic pencil.
Always be aware.

Rule no. 6
When it is necessary to handle equipment that is plugged in, be sure hands are dry and, when possible, wear nonconductive gloves, protective clothes and shoes with insulated soles.
Remeber: gloves, clothes and shoes.

Safety clothes, gloves and shoes
Safety clothes, gloves and shoes

Rule no. 7
If it is safe to do so, work with only one hand, keeping the other hand at your side or in your pocket, away from all conductive material. This precaution reduces the likelihood of accidents that result in current passing through the chest cavity.
If you ever read about current passing through human body you will know, so remember – work with one hand only.
If you don’t clue about electric current path through human body, read more in following technical articles:

Rule no. 8
Minimize the use of electrical equipment in cold rooms or other areas where condensation is likely. If equipment must be used in such areas, mount the equipment on a wall or vertical panel.

Rule no. 9
If water or a chemical is spilled onto equipment, shut off power at the main switch or circuit breaker and unplug the equipment.
Very logical. NEVER try to remove water or similar from equipment while energized. Afterall, it’s stupid to do so.

Rule no. 10
If an individual comes in contact with a live electrical conductor, do not touch the equipment, cord or person. Disconnect the power source from the circuit breaker or pull out the plug using a leather belt.
Tricky situation, and you must be very calm in order not to make the situation even worse.
Like in previous rules – Always disconnect the power FIRST.

Always disconnect the power FIRST
Always disconnect the power FIRST

Rule no. 11
Equipment producing a “tingle” should be disconnected and reported promptly for repair.

Rule no. 12
Do not rely on grounding to mask a defective circuit nor attempt to correct a fault by insertion of another fuse or breaker, particularly one of larger capacity.

Rule no. 13
Drain capacitors before working near them and keep the short circuit on the terminals during the work to prevent electrical shock.

Rule no. 14
Never touch another person’s equipment or electrical control devices unless instructed to do so.
Don’t be too smart. Don’t try your luck.

Rule no. 15
Enclose all electric contacts and conductors so that no one can accidentally come into contact with them.
If applicable do it always, if not be very carefull.

Rule no. 16
Never handle electrical equipment when hands, feet, or body are wet or perspiring, or when standing on a wet floor.
Remeber: Gloves and shoes

Rule no. 17
When it is necessary to touch electrical equipment (for example, when checking for overheated motors), use the back of the hand. Thus, if accidental shock were to cause muscular contraction, you would not “freeze” to the conductor.

Rule no. 18
Do not store highly flammable liquids near electrical equipment.

Rule no. 19
Be aware that interlocks on equipment disconnect the high voltage source when a cabinet door is open but power for control circuits may remain on.
Read the single line diagram and wiring schemes – know your switchboard. 

Rule no. 20
De-energize open experimental circuits and equipment to be left unattended.

Rule no. 21
Do not wear loose clothing or ties near electrical equipment. Act like an electrical engineer, you are not on the beach.

Example of human stupidity and ignorance of basic safety

Electrical safety, come on… I guess we’ll never know did the cord extension drop into water… Hope not.

Example of stupidity
Example of stupidity

Do You Understand What Is Electric Shock?


Electric shock danger sign
Electric shock danger sign


Electric current passing through the body, particularly alternating current at power frequencies of 50 Hz and 60 Hz, may disrupt the nervous system, causing muscular reaction and the painful sensation of electric shock. The most common reaction is to be thrown off the conductor as a result of the muscular contraction.
However, in a small number of instances, the consequence is death from cardiac arrest, or from ventricular fibrillation (where the heart muscle beats in a spasmodic and irregular fashion) or from respiratory arrest.
The psychological effects are largely determined by the magnitude and frequency of the current, the waveform (for example, continuous sine wave, or half wave rectified sine wave, or pulsed waveform), its duration, and the path it takes through the body.
An authoritative guide on the topic is published in IEC 60479. The following text concentrates on the most common situation of a shock from a continuous power frequency ac waveform.
The magnitude of the current is the applied voltage divided by the impedance of the body. The overall circuit impedance will comprise the body of the casualty and the other components in the shock circuit, including that of the power source and the interconnecting cables. For this reason, the voltage applied to the body, which is commonly known as the touch voltage, will often be lower than the source voltage.
The impedance of the body is determined by the magnitude of the touch voltage (there being an inverse relationship between impedance and voltage) and other factors, such as the wetness of the skin, the cross-sectional area of contact with the conductors, and whether or not the skin is broken or penetrated by the conductors.
As a general rule of thumb, at an applied voltage of 230 V at 50 Hz, the total body impedance for a hand-to-feet path will be in the range 1000 Ω to 2500 Ω for most of the population, falling to around 750 Ω at voltages in excess of about 1000 V.
Depiction of a typical indirect contact electric shock
Figure 16.1 - Depiction of a typical indirect contact electric shock

The path that the current takes through the body has a significant effect on the impedance. For example, the impedance for a hand-to-chest path is in the order of 50 per cent of the impedance for a hand-to-foot path. Moreover, the current’s path through the body is a significant determinant of the effect on the heart.
Table 16.1 summarizes the physiological effects of current passing through the body.
The effects relate to a hand-to-hand shock exceeding 1 s for a person in good health. If the duration were less than 1 s, greater currents could be tolerated without such adverse reactions.
Electric shock accidents are most common on low-voltage systems and are usually subdivided into two categories of direct contact and indirect contact shocks. A direct contact shock occurs when conductors that are meant to be live, such as bare wires or terminals, are touched. An indirect contact shock occurs when an exposed conductive part that has become live under fault conditions is touched, as depicted in Fig. 16.1.
Examples of an exposed conductive part are the metal casing of a washing machine and the metal casing of switchgear. This type of accident, which requires two faults to occur (the loss of the earth connection followed by a phase-to-earth fault), is quite common.

Physiological Effects

Table 16.1 The effect of passing alternating current (50 Hz) through the body from hand-to-hand
Current (mA)Physiological effect
0.5–2Threshold of perception
2–10Painful sensation, increasing with current. Muscular contraction may occur, leading to being thrown-off
10–25Threshold of ‘let go’, meaning that gripped electrodes cannot be released once the current is flowing. Cramp-like muscular contractions. May be difficulty in breathing leading to danger of asphyxiation from respiratory muscular contraction
25–80Severe muscular contraction, sometimes severe enough to cause bone dislocation and fracture. Increased likelihood of respiratory failure. Increased blood pressure. Increasing likelihood of ventricular fibrillation (unco-ordinated contractions of the heart muscles so that it ceases to pump effectively). Possible cardiac arrest
Over 80Burns at point of contact and in internal tissues. Death from ventricular fibrillation, cardiac arrest, or other consequential injuries

First Aid with Emergency Defibrillator

First aid - Emergency defibrillator
First aid - Emergency defibrillator

When providing first aid to an electric shock casualty, the first action should be to remove the cause by switching-off the supply or otherwise breaking contact between the casualty and the live conductor. Cardiopulmonary resuscitation may be required.
If the casualty is suffering from ventricular fibrillation, the only effective way to restore normal heart rhythm is by the use of a defibrillator.
Where a defibrillator is not immediately available, the first aider should carry out cardiopulmonary resuscitation until either the casualty recovers or professional assistance arrives.
SOURCE: J.M. Madden

Thursday, May 14, 2015

The origins of field placement names in cricket

Cricket fielding positions
For ardent cricket followers over the years, the term ‘point’ can easily be associated with the man stationed for the cut shot. Or in simpler words, the cult figure of Jonty Rhodes refusing to allow anything within touching distance of him to go through. Similarly, the word ‘slip’ instantly leads to the mind imagining Shane Warne or Mark Waugh wearing their round hats, waiting to gobble up anything that Glenn McGrath or Brett Lee manage to get an edge off.
But have you ever wondered why the ‘slip’ is called a slip? Or why the ‘covers’ are named so (what do they cover anyway)? One of many interesting names is the ‘third man’ (wait, where are the first and second men?). Or the Indian favourite ‘gully’ (not to be construed to have any relation to ‘gully cricket’).
Let us try to see the origins of a some of these apparently funny names. Or should we use the term ‘silly’ names?

The ‘on’ and ‘off’ side

Not to be confused with a switch, and not applicable in case of a switch hit either. This is the gospel on which further discussions will be based. The etymology of the off side and on side in cricket predates to the 19th century, when transport was done via carriages and not motor vehicles. This was bought into the cricket field, for reasons not entirely clear.
It actually began as ‘off-side’ and ‘near-side’, rather than the more popular term ‘leg-side’ that is in use today. The ‘off-side’ was the opposite side of where the rider would walk or mount, the leg-side or ‘near-side’ being the other end. This way, the field got divided into two halves – when you play away from your legs, it is the ‘off-side’, and if it is nearer to the legs, the ‘leg-side’.
Before we move further, let us see a diagrammatic representation of the field placements. Starting with the slips, we will go clockwise from one position to another.

Fielding positions

Slips – One of the more logical names on the cricket field. This probably began when the captains started asking their fielders to stand next to the keeper to take advantage of any ‘slip’ (read ‘mistake’) from the batsman. In due course, the term was coined on the basis of its literal meaning.
Point – We are skipping the gully and third-man here, but don’t worry, it is for good reason. The term ‘point’ was coined from the phrase “near the point (direction of the face) of the bat”. This is a clear indicator of the fact that the ‘point’ in early days was a more close-in position than the one we are used to seeing today, at the edge of the circle.
Gully – This stems from the literal meaning of the word ‘gully’, which is ‘a narrow channel’. The slips and the point were close catching positions but soon the captains realised that the ball often passed through the gap between these fieldsmen. To plug this ‘gap’ or ‘gully’, they employed another fieldsman in that area.
Third man – It is important to understand here that the ‘gully’ and ‘third man’ are contemporary positions; each came about with no knowledge of the other existing. With the slip and point patrolling the offside behind the square, for the same reason as mentioned above, i.e. to stem the gap between them, a ‘third’ fielder was employed (traditionally closer than what we have come to terms with). This fielder soon came to be known as the ‘third man’.
Covers – There are two theories to this position; the first claims that the fielder is stationed where traditionally the pitch covers were kept post-play, when not in use. So the captain instructed his fielders to stand near the ‘covers’, leading to its modern nomenclature.
The other theory, in line with the earlier origins, claims that the ‘covers’ was a fieldsman who covered the ‘point’ and ‘middle wicket’.
Before we go to the other field placements, let us take a detour and define a few rather well-known words.
Long/Deep-X – Farther away from the batsman
Short-X – Near (short distance from) the batsman
Silly-X – So close to the batsman, it is ‘silly’ or ‘imprudent’ to be standing there
For other terms, one can refer to the glossary in the image above.
Mid-on and Mid-off – There is general misconception that these terms refer to the ‘middle-ness’ of the position, i.e. they are not too far away from the batsman, nor too close. However, this is far from the truth. The terms 'mid-onand 'mid-offstem from the terms ‘middle wicket off’ and ‘middle wicket on’ used earlier.
The ‘middle wicket’ was a player stationed on the off-side between extra cover and the bowler. Soon, the occasional need for the same fielder on the leg side came up, and to differentiate between the terms, they were suffixed with ‘on and off’.
The terms ‘long-on’ and ‘long-off’ were analogous to mid-on and mid-off, but farther away from the batsman and nearer to the boundary.
Mid-wicket – This term has a peculiar history. Though a traditionally used term, it received its current meaning somewhere in the 1930s. Prior to that, it was simply another name for ‘middle-wicket off’, the more commonly used field position of the two.
Fine-leg and Square-leg: The term ‘fine’ means ‘straight’ i.e. nearer to the line that can be drawn between the stumps of the strikers’ and non-strikers’ end. The term ‘square’ means nearer to the line of the batting crease. In simple terms, if a player is standing near the ‘square-leg umpire’ he is in a ‘square’ position and if he moves towards ‘fine-leg’, he is getting ‘finer’.
The terms fine-leg and square-leg are now easy to understand; if a batsman hit the ball bowled nearer to his leg ‘square’ on the on-side, it would be fielded by the ‘square-leg’ position and if his hit is finer, it would go towards the direction of ‘fine-leg.’
So there you have it; this is how the most commonly used fielding positions received their names. The others, such as deep-square leg or forward-short-leg, stem from the direction, distance and orientation of the position; for example, forward denotes the fielder ahead of the batsman (as opposed to backward), ‘short’ indicates the proximity of the player near the bat and ‘leg’ denotes that the fielder is stationed on the ‘leg side.
If you wish to know more about any other fielding position, leave a question in the comments below and we will try to give an answer to the best of our knowledge.

Sunday, February 8, 2015

Here are 11 things they definitely never taught you in school:


7. How Michael Jackson actually defied gravity:

via BoomsBeat

 1. How filming in green screen works:

via imgur / trophygeek

2. How ice cream sandwiches are made:

via imgur | reddit/u/NTRX

3. How a top-loading washing machine works:

via imgur | reddit/u/CaliforniaPoppyCock

4. How zippers work:

via imgur | reddit/u/kimcen

5. What it looks like when you drink water:

via imgur | reddit/u/Click here

6. How ice cream cones are made:

via imgur | reddit/u/olegsfinest

8. How fans oscillate:

via Shock Mansion | reddit/u/Spackkle

9. How a key opens a lock:

via Gizmodo

10. How WiFi travels in your apartment:

via 9gag

11. How ants walk:

via imgur | reddit/u/thestamp

12. How paperclips are made:

via gfycat | reddit/u/jaycrew

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