From Ideas to Implementation

From Ideas to Implementation:

1) Metal lattices consist of positive metal ions, to maintain stability the electrons are free moving (delocalised) these electrons are what allow the metal to be conductive.

2) The way that an object can be defined into the three categories which are conductors, insulators and semiconductors is by their electric conductivity. This is then based on the energy band level which is determined by the band gap between the conduction band and the valence band. The difference between conductor's insulators and semiconductors is the effect on the electricity when electricity is sent through the object. The electrical conductivity is determined by the electrons in the atom as the electros are said to occupy particular energy levels. Conductors are from the highest energy band which means that they partly fill the valence band and have empty levels which allows the electrons to move freely under the influence of an electric field. Insulators on the other hand completely fill the valence band which means the electrons cannot move freely which prevents them from conducting the electricity from the electric field. In semiconductors the gap between the conduction band and the valence band is smaller than the insulator but larger than conductors. From this you can see that it is possible to conduct electricity but not as well as the conductors this is because the electrons are closer together and have less room to move around which means they are not the best conductors for electricity.

3) Electrons that move in a nearly full band creates what is known as a 'hole'. This means there is one less valence electron and another electron can now move to cover this hole creating another hole and the cycle continues as the holes will not all be filled. With the electrons moving from hole to hole in this cycle it means that all the electrons are travelling in one direction with the holes travelling in the opposite direction (as they cannot travel same ways due to the fact that the electrons are covering the holes when needed).

4) In conductors the number of electrons that are moving between the conduction band and the valence band are is of a high number which means that there is a lot of room for the electrical current to travel through. Temperature plays an important role in the electrons as slight temperature changes can cause the electrons to travel into the conduction band making the object more conductible. For example in semiconductors if the heat rises the electrons would travel into the conduction band making the object conductible.

5) Germanium was used as a semiconductor as it was simple to purify as the equipment to purify other semiconductors was not at its peak as such. The semiconductor that is mostly used today is silicon as it is cheap easy to form the shape required it can stand relatively high levels of heat and is stronger than germanium.

6) Doping is used to make semiconductors more conductible so it can handle the electric current better it increases the amount of holes or electrons so that they can move more freely thus meaning semiconductors will last longer. When doping takes place the atoms that are added have to be done to the right ratio and need to fit well enough so that the electron flow does not get distorted.

7) The difference between P-type semi conductors and N-type conductors is that in P-type there are more positive holes than negative charge carriers, while N-type semi conductors are the opposite with more negative charge carriers

8) The difference between solid state and thermionic devices is that a thermionic device requires a vacuum for the electrons to be able to flow efficiently between the electrodes, while a solid state device works in normal temperatures. Another advantage of using a solid state device is that it does not require a heating circuit but a thermionic device requires the heating circuit to be able to emit the electros. The main reasons that solid state devices have taken over thermionic devices is that the solid state device is smaller cheaper and easier to use, it always works immediately and requires less power. For these reasons solid state devices are more used for electronic manufacturers rather than the thermionic device.

Medical Physics:

1) The difference between ultrasounds and normal hearing range is that the frequencies, audibility, wavelengths are very different. Normal hearing range has a frequency of 20 Hz-20 kHz while ultra sounds are all over 20 kHz and can be 1MHz- 15MHz in the case that they are going to use it for medical imaging. Humans can also hear normal sound but when it comes to ultrasounds the sound cannot be heard by human ears,