Combustion (burning of fuel) can be classified into two: complete and incomplete.

 Combustion of the fuel will be complete when there is sufficient quantity of oxygen for the fuel to burn. These results in a blue flame and the heat generated will be maximum. Combustion is termed incomplete when the oxygen supply is insufficient. This results in a yellow flame. As a result, the heat produced is lesser than the maximum obtainable from the fuel.

In the case of a candle flame, as one can see, there are three distinct zones. The hottest zone surrounding the wick is blue in colour. A zone of unburnt volatile fuel forms the centre of the flame. The yellow luminous zone which is responsible for illuminating the room forms a major portion of the flame. This zone contains hot carbon particles which get heated by hotter zone below. They emit light due to incandescence. As they move out of the flame and escape into the air, they get oxidized and cooled. The process continues as more fuel is burnt.

In the case of LPG (liquefied petroleum gas, which is mostly propane and a little butane), the aim is to get the maximum heat energy from the fuel so that the cooking time is reduced and fuel conserved. Hence the incoming gas is mixed with sufficient quantities of air in the burner and then burnt to give a blue flame.

It is known that propane needs about 25 times its volume for complete combustion. Hence by designing the pinhole (which lets the gas into the burner) suitably, the flow of gas is controlled and ratio of gas and air is maintained. As there is no incandescent zone the flame does not illuminate the room. But, sometimes we see that dust and rust block the holes preventing free flow of air. This results in a yellow flame which illuminates the room just like the candle flame.

Also in the case of LPG stoves, as all the fuel that is injected is burnt fully, the heat generated is more and the cooking time is reduced.

An atom bomb is a fission device. Here a heavy atom (such as uranium) is split into two or more lighter atoms. In such a nuclear fission process, one or two neutrons are also released from each atom. If these neutrons are captured by the surrounding heavy atom, further fission takes place leading to further neutron release. In atomic power reactors, this chain reaction is controlled so that the energy released during the reaction can be used beneficially.

But in the case of an atom bomb, the chain reaction is not controlled but left free. This leads to the release of large amounts of heat energy in a very short time resulting in a catastrophic explosion.

In a fusion bomb, such as the hydrogen bomb, two or more lighter atoms fuse together to form a heavier atom. Such fusion reactions can take place only at very high temperatures; say a few million degrees Celsius.

Only at such temperatures can the starting atoms overcome the repulsive forces acting between them.

 In this case also, when uncontrolled fusion takes place a large amount of energy is suddenly released resulting in an explosion far bigger than an atomic explosion.

 It may be noted that the temperature needed to initiate a fusion reaction is normally obtained by a fission reaction.

            The major component of milk is water (83-87%). Its other constituents are protein (3.5%), sugar (5%) and fat (4-7.4%). When heated, fat being lighter than water, floats as a creamy layer on the top and water vapour, in the form of steam bubbles, is trapped under it. Further heating results in the formation of more number of bubbles. These bubbles expand and lift the creamy layer causing it to overflow. In the case of water, the steam bubbles break as                                                                                          they reach the surface.

 Hearing aid is an electronic device used by those who are hard of hearing, to amplify sounds particularly speech. It’s essential components are a microphone, an electronic amplifier and a receiver, all operated by a battery. In simple terms, the hearing aid can be likened to a miniature public address system. Sounds are amplified by the amplifier and the output is fed to the receiver.

The gain and amplification of the device is determined by the amplifier. In fact, there are low gain, moderate gain and high gain hearing aids. We know that sound signals are wave patterns in which air molecules vibrate, and waves representing different sounds differ in their wave length (and frequency).

As the human ear can selectively respond to certain frequencies very well and not so well to others, manufacturers vary the frequency response of hearing aids with electronic filters, based on the audiometric configurations (low frequency, high frequency or flat loss of hearing) of the user.

Externally most of the aids are provided with a battery compartment, on- off switch, tone control (to adjust the frequency response) and a volume control (to adjust amplification).

In some aids the on-off switch will be provided with a telephone setting to enable the individual to use the telephone. This is made possible with a telecoil in the aid which selectively picks up telephone signals.

GPS is a system which shows the exact position on the earth, anytime in any weather and anywhere. There are 24 GPS satellites orbiting at 11,000 nautical miles above the earth. They are continuously monitored by ground station located worldwide. The satellites transmit signal that can be detected by anyone with a GPS receiver. Using the receiver one can determine the exact position namely longitude, latitude, altitude and the time, with greater precision. GPS has 3 parts: the space segment, user segment and the central segment.  Space segments consists of 24 satellites as stated above. User segment consists of receivers which we can hold in hand or mount in a car and this gives the exact location on the earth. The control segment consists of ground stations that make sure that the satellites are working properly.

The satellites are equipped with precise clocks that keep accurate time to within 3 nano seconds (3×10-9 secs). The time signals are transmitted along with their orbital parameters. The receiver detects the time signal and calculates the distance of the satellite. By getting the signals from three different satellites and by doing mathematical calculations, the receiver is able to give the exact position where the receiver’s located. By getting the information from fourth satellite, it is able to give the time also.

Thus four satellites are required to compute the four dimensions of x, y, z (position) and time. At any time and at any location always a minimum of four satellites will be visible for the receiver.

Global Positioning System (GPS) works on set of navigational satellites (18 to 21 nos) around the earth in orbit and their signals to a receiver on earth. The signal from each satellite provides the position of the satellite at a specific time.

The receiver software analyses the signals and displays the position of the receiver with reference to a specific spherical coordinates, which has, its centre of earth as its origin.  The navigational satellites are so orbiting that at any given time and spaces on the earth, a minimum of three are visible to the receiver. 

 The accuracy of the position increases with the number of satellites the positional accuracy is around 200 NV, with a different correction (a method of using two or more receiver) the accuracy can be increased to centimetres. Ifs are has been increasing since Iraq war, especially in all modes transportation.  

The Global Positioning System is a satellite based Radio Navigation System developed by the United States Department of Defence. It provides continuous, all weather worldwide navigation capability for sea, land and air applications.

The user can easily determine his position, i.e. latitude, longitude and altitude using the GPS receiver which receives signals from various satellites orbiting the earth. ‘Tie complete GPS constellation consists of 21 operational satellites and 3 spares, orbiting the earth about once every 12 hours at a distance of roughly 10,900 nautical miles.

 Unlike ground based navigational system signal generators the satellites are able to cover a very large area of the earth because of their altitude and the fact that their signals are free of interference from local geography. The error in GPS at times may come up to 30 to 100 Mts.

An advanced system known as GDPs or differential Global Positioning System evaluates this error with an accuracy of within 5 Mts.