Why is the nib of a fountain pen split?

Why is the nib of a fountain pen split?

A fountain pen allows a controlled flow of ink because of its specially designed flow system for ink and air. The flow system consists of an ink reservoir, a feed bar (also called feed) and a metal nib. 

The nib is split starting from a breather hole till the tip to form two tines (branches). The feed has a longitudinal flow channel on its top surface starting from the inside end almost up to the forward end and it is covered by the nib. The channel is a broad groove and along its floor are cut two or more narrower grooves (called fissures). The broad channel brings ink up to the breather hole and the split of the nib. The split carries the ink to the tip and paper. The channel allows an occasional flow of air in the opposite direction into the reservoir so that pressure there does not decrease too much due to emptying of the ink. When such an air-flow takes place the fissures still contain ink and enable immediate filling of the channel. The nib tip has a special shape consisting of two hemispherical ends at the bottom of the tines. Ink forms a meniscus between these two rounded parts and spreads on paper as soon as a contact is established. The split width will change if pressure is applied and this will change the flow. The feed often has slots, combs or other design elements so that the capillary action can draw ink and hold it to have a steady flow or to avoid an overflow. Even when a pen is not used for a while, capillarity replenishes through the split, the evaporated ink and the pen is kept ready. The capillary force that maintains a continuous ink flow also helps to support ink from dripping due to gravity while not writing.

Source: thehindu.com

How does the human body react to a severe electric shock?

How does the human body react to a severe electric shock?

The human body contains body fluid mainly consisting of water, which gets electrolysed on passage of electric current in the event of an electric shock. This leads to other more complex electric effects in the body as follows:When an electric current passes through a living tissue the nerves respond in a typical way that makes the muscular tissues contract and a twitching is noticed as was observed by the famous Italian scientist Luigi Galvani in the 1780s.In fact, the symptom of such spasms has been recorded in more controlled experiments where a definite quantity of electric charge was deposited on the spinal cord of frogs and the frogs exhibited the same type of spasms in their muscles; more charge resulted in greater twitching of muscles. In the human body also, the same effect takes place. In severe cases of such electric shock, the spasms can be so strong that the muscles of some critical organs like the heart can be thrown out of their characteristic rhythmic motion. And the electric current can also disrupt the functioning of the brain. The combined effect can be fatal.

Source: thehindu.com

Why does the filament of a bulb burn out when exposed to atmosphere whereas that of a heater coil does not?

Why does the filament of a bulb burn out when exposed to atmosphere whereas that of a heater coil does not?

Both bulb and heater work on the principle of light or heat being generated, when a current passes through a conductor having a finite resistance. Oxidation reaction, that is, chemical reaction of an element with oxygen to form new compounds, is responsible for the bulb's filament burning out. The main important factors influencing this are the temperature and the environment of operation, as well as the chemical nature of the conducting wire. 

In the case of bulb, formerly known as 'incandescent bulb,' the light (electromagnetic radiation) is radiated out, when the filament is heated to very high temperatures (around 3,000 degrees Celsius). The filament is made of a tungsten wire of very small diameter (less than that of a human hair), made into long spiral or spring-like structure (when fully extended, the length can be up to a few feet). Due to this coiled nature of the wire, it offers high resistance to the electrical current, thereby heating up to a very high temperature. Under these conditions, if it is exposed to atmosphere, tungsten filament will react with atmospheric oxygen to form tungsten-oxides. So as to prevent this deleterious process, which can limit the lifetime of the filament, the filament is sealed in vacuum or in inert gas environment. 

In the case of heater, the filament is made of Nicrome alloy (an alloy of nickel and chromium). Since the operating temperatures are in the range of a few hundred degrees Celsius, the required electrical resistance is relatively small and hence, the wire diameter is typically in millimetres and the length is relatively small. Firstly, the temperature of operation of a heater is rather significantly less compared to the bulb and secondly, the alloy is more resistant to chemical oxidation compared to tungsten. Hence, it endures long-term operation under ambient conditions.

Source: thehindu.com

Why do air bubbles cling to the walls of a vessel when water is heated?

Why do air bubbles cling to the walls of a vessel when water is heated?

When water is heated, steam bubbles out. Apart from the energy required to heat up to the boiling point (about 100 °C) and the latent heat, additional energy is required (due to surface tension) to form the bubbles since they have a free surface.Pressure inside a bubble is higher than that in the surroundings by an amount 2 T/R, where T is the surface tension coefficient and R is the radius of the bubble. If R is very small this additional pressure can be very large. Hence the bubbles are usually formed where the hot vessel surface is rough and has crevices. 

One can observe boiling water on a stove where the steam bubbles rise from a rough horizontal surface of the vessel. When the bubbles rise due to buoyancy they grow in size and when they are located over the water surface they are formed by a film and have two free surfaces an inside one and an outside one. Additional pressure inside the bubble is then given by (4 T/R) due to two surfaces. Interesting things happen here. This liquid film is fragile and can easily break unless it is made up of milk or oil or soap water. When a bubble comes close to another bubble or an object it gets attracted and clings to it because of surface tension. We can see bubbles clustering on the free surface of coffee. The bubbles in the interior of the water body cling to the wall and have the shape of a truncated sphere. To detach them, there is a need to increase their surface area, which needs additional work. Thus they stick to the wall because of surface tension, resisting buoyancy force or any other disturbance. Since they do not have a film they do not break.Such bubbles can be a great nuisance in a water flow experiment when observations are to be made through a glass window, for example, by shining a laser beam. Bubbles arising from the dissolved air and sticking to the glass window cannot easily be removed even by increasing the water flow rate. They need internal mechanical wiping.

Source: thehindu.com

How are the temperatures below zero degrees celsius measured?

How are the temperatures below zero degrees celsius measured?

Image Source: dexter.lib.mi.us

Mercury thermometer is used to measure temperatures above zero degree Celsius. Mercury expands upon heating and is a good thermal conductor. It is also a bright liquid and thus convenient for temperature measurement. However, mercury cannot be used because it freezes and stops flowing at minus 38.87 degrees Celsius. Measurement of subzero temperatures are necessary in many areas. These include weather (daily temperatures of towns in Himalayan and such snow-covered regions), processes such as freeze drying to make milk powder, immunology where vaccines have to be preserved and so on.

Temperatures below zero degree Celsius (that is, the minus scale) can be measured by resistance thermometers. They work on the premise that the resistance of materials changes with temperature. Resistance decreases as the temperature is reduced in the case of metals (positive temperature coefficient), while the resistance increases with decrease of temperature in the case of semiconductors (negative temperature coefficient). Platinum resistance thermometers are used down to minus 170 degree Celsius. For measurement of even lower temperatures, Germanium and Silicon diode (semiconductor) thermometers are used. Thermocouples can also be used for measuring temperatures below zero degrees

Source: thehindu.com

Why is milk white?

Why is milk white?

Before we can answer why milk is white, we need to explain why anything at all appears white. It is just a matter of simple physics. The reason why items appear white is because they reflect all light wavelengths and absorb none. If all wavelengths of light were absorbed and not were reflected back, the object would appear black.

Image source : health.clevelandclinic.org

While milk is primarily composed of water (approx 87%), which is a colourless liquid; there are other components of milk (fat, protein, lactose, minerals and vitamins) that influence the colour of milk. The fat and protein molecules in the milk reflect light at a wavelength that makes the liquid appear white.

If we were to remove some of the fat from the milk (like in skim milk), it would give the milk a different colour because of the wavelengths the light is reflecting back to our eyes. That is why skim milk has a bluish tinge.

Source: albertamilk.com

A fly in mid-air in the front side of a moving vehicle should come back to the rear side. But the fly remains in the same location in the air. How?

A fly in mid-air in the front side of a moving vehicle should come back to the rear side. But the fly remains in the same location in the air. How?

All objects on earth, including men, insects, buses, trees, buildings, lakes and atmospheric air are struck to earth’s gravity because the latter operates a force towards the centre of the earth from the centres of gravity of each of the objects in the earth’s gravitational field. Since the gravitational attraction among the objects is negligible in comparison to the gravitational pull the earth exerts on each object in its field, the mutually relative positions of these objects remain unchanged. Thus, the earth provides an inertial frame of reference for the objects it holds in its field. The mutual and relative positions of the objects would change only when one or more of these objects make a resultant displacement overcoming the gravitational pull.

Image source : spirit-animals.com

According to Newton’s First Law of Motion, an object in stationary state or one in a state of uniform velocity in an inertial frame of reference will continue to be in that state unless and until a force acts on it. This retention of state in the absence of a net force is called the inertia of the object, originating by its own mass. Thus, all the parts and material objects physically linked to the vehicle’s framework retain their positional coordinates as long as they do not make any relative displacement with respect to the vehicle’s internal inertial frame of reference. When a vehicle is moving with certain speed, the objects, materially connected to the vehicle, also move along with the vehicle due to inertia as the whole vehicle serves as the inertial frame of reference. These objects include not only the passengers, seats, luggage, etc., but also the air inside it.

An insect is no exception for this inertial influence. It needs air to fly and the air it flies in is also moving with the same speed as the bus. If the fly does not make any forward or backward movement it remains in the same location because the fly is materially (and inertially) connected to the vehicle through the air. Imagine stationary vehicle with its air removed by evacuation before a (super) fly is suspended in the bus with no forward or backward movement. If the vehicle, then suddenly, commences a forward movement, the fly would really hit the back of the vehicle because now there is no air that goes along with the vehicle holding the fly, materially and inertially stuck to the vehicle’s frame of reference.

What Is Superconductivity?

What Is Superconductivity?

Answer 1: 

The electrical resistivity of some metals and alloys drops suddenly to zero when their specimens are cooled to a low temperature in liquid helium range. This was first observed by K. Onnes in 1911 in mercury.

The resistivity of mercury vanished completely below 4.2 degree Kelvin. The transition from normal conductivity occurs over a narrow range of temperature of order 0.05 degree Kelvin. This phenomenon is referred to as ``superconductivity.'' The specimens are called superconductors.

Thus, superconductors are materials which possess much more than infinite conductivity . They are perfect electrical conductors under special conditions. Superconductivity occurs in many metallic elements of the periodic table.

Experimental facts regarding superconductors revealed that if a superconductor has the form of a ring, a current can be induced in it by electromagnetic induction, then this current continues to persist with undiminished strength for days. This is ``persistant current.

Answer 2:

At low temperatures, metals have high conductivity of electricity, showing low resistance to the passage of current. The electrical resistance of metals decreases with decrease in temperature.

Superconductivity reveals that it is not confined to a few metals or alloys, but may be present in all metals and alloys provided they can be cooled to temperatures nearer absolute zero. K. Onnes noticed that at 4.2 kevlin the electrical resistance of pure mercury (Hg) became nil and the metal acquired the property of superconductivity.

The temperature at which the metal acquires high conductivity or superconductivity is known as transition temperature (Te). It has been illustrated that a current of about 1000 amperes passing through a tin wire at about 3K shows no heating at all.

Published in The Hindu on Nov 8, 2001.