Modern Physics
Chapter
6
1- The electromagnetic waves:
* They consist of
two fields, magnetic and electric, normal to each other and to the
direction of propagation. They are transverse waves.
* Can
propagate through vacuum with a speed c = 3 x 10 8
m / s.
* They reflect, refract, interfere and diffract.
2-
Cathode Rays:
* Invisible rays emitted from the "cathode"
of a tube contains gas at a pressure of 0.01 m m Hg.
* They
travel in straight lines, deflect in magnetic and electric fields and
have mass, momentum & charge.
3- Thomson's Experiment
to determine
for
electrons:
4-
Millikan Experiment to determine the charge of an electron:
5-
The proton:
6-
The neutron: "Chadwick's Experiment":
7-
The atomic spectra:
8-
Continuous spectrum:
Is that spectrum that contains all the
possible wave lengths in a given range.
9- Laser: is an
acronym for; "Light Amplification by Stimulated Emission of
Radiation".
* Characteristics of laser beam:
i-
Highly monochromatic.
ii- Highly directional.
iii- Highly
coherent.
10- The half-width of spectral line: "HWSL"
11-
Fundamentals of laser operation:
* The number of atoms exist in
the higher energy level is much greater than those in ground level.
* The stimulated emission is the predominate type of emission.
* Doing enough arrangements to insure that most of the emitted
photon emerge in the same direction.
12- The "Pumping"
processor:
* Is the process of imparting energy to the working
substance of a laser, to transfer the atoms into the excited state.
13- The "Ruby Laser":
* It consists of:
i- A ruby rod, its two bases are well polished, parallel and
firmly normal to the rod axis.
ii- A xenon tube.
iii- A
cooling system uses liquid air.
* The produced beam is pulsed
and in the red region of light.
14- Types of laser:
*
Gas laser.
* Crystal laser.
* Semiconductor laser.
*
Liquid laser.
15- According to the nature of
emission: * Continuous rays. * Pulsed rays.
Chapter 15
1- A metallic crystal consists of positive ions and a cloud of free electrons roaming around the crystal in random motion. There is a force of attraction between the ions and the electron cloud. But the resultant of all forces of attraction on a single free electrons is zero. If an electron tries to escape from the metal, a net force of attraction due to the atom layer at the surface pulls it in. 2- A pure silicon (semiconductor) crystal consists of atoms covalently bonded. At low temperatures, there are no free electrons. If temperature increases, some bonds are broken, electrons become free, leaving behind holes move randomly. 3- The number of broken bonds increases with temperature. It may increase also by an external stimulus, such as light, provided that the photon energy is sufficient to break the bond. 4- The number of free electrons and holes increases by adding impurities (doping). Thus, the material becomes n-type or p-type. 5- The conductivity of a semiconductor depends on the conduction of free electrons and holes. Thus a semiconductor has two current carriers: electrons and holes, while in a metal there is only one current carrier (the electron). Electron concentration in a metal is constant and does not depend on temperature. 6- Semiconductors are environment - sensitive. They can be used as sensors to light, heat, pressure, humidity, chemical pollution, radiation…etc. 7- A diode (pn junction) consists of a p-type region and an n-type region. If the p-side is connected to the positive terminal of the battery and the n-side to the negative terminal (forward connection or forward bias) current flows. If the battery is reversed no current flows. This is why a diode is used in rectification. 8- A transistor may be pnp or npn, and can be used as an amplifier, since the ratio of the collector current to the base current e is large. Therefore, any small change in the base current leads to an amplified change in the collector current. 9- A transistor may also be used as a switch. It is used in logic gates, such as an inverter (NOT, AND, OR) gates. 10- Digital electronics is superceding analog electronics for its ability to overcome electrical noise. Its basic concept is to code. Information in binary form (0, 1). 11- ICs have the advantage of small size and weight, increased speeds and capacity, and yet low cost. This is the reason for the proliferation of PCs.