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

A fused electric bulb has its filament cut. Why?

A fused electric bulb has its filament cut. Why?

A filament based electric bulb generates light through a process called incandescence meaning glow associated with a hot-body. Hence this type of lamps are called incandescent lamps. The electric bulb we normally use consists of a coiled filament made of tungsten wire (essentially an electrical resistor) of different thicknesses depending on the power ratings of the lamp. 

When the lamp is switched on, an electric current passes through the resistor producing a lot of heating called Joule heating. When the filament is heated to near white-hot, its body temperature rises to a few thousand (s) degrees centigrade which in turn take the tungsten filament near its melting/vaporisation point. On continued usage, this vaporisation leads to loss of the tungsten material making it thinner and thinner at some points along the length of the filament coil. 

In order to minimise the vaporisation loss, the whole filament system is enclosed in an evacuated (or filled with inert gases) glass envelope (bulb). When the electric bulb is switched on and off several times, its filament is taken through several cycles of heating and cooling leading to the filament getting worn-out at some points that would result in the filament getting cut at these point(s). This would eventually make flow of current along the filament and hence the incandescent-glow from the bulb impossible.

Source: thehindu.com