2.0 INTRODUCTION OF PHYSICS
We see and hear by means of light and sound wave travel to aerials through the air from television transmitter. Although we cannot see light, sound and radio waves, the travel across enormous distance of empty space.
2.1 WAVES
Consider a group of swings in playground swing set. We know that each swings itself behaves like simple pendulum, that is like an oscillator. Now, let’s connect the swing to one another. To be specified, suppose we tie a rope from the seat of the swing to its neighbor and then another rope from the second swing to the third may propagate around the swing, and so on. When the swing is at rest, in equilibrium, the connecting rope has no effect. If you now seat on the first seat and begin oscillating as well. You have created a traveling disturbance.
In general, a disturbance that propagates from one to another is referred to as a wave. Waves propagate with well in define speeds determines by the properties of the material through which they travel. In addition, waves carry energy. For example, part of the energy you put into sounds waves when you speak is carried to the ears of others, where some of the sound energy is converted into electrical energy carried by nerve impulse to the brain, in turn, created the sensation of hearing.
It is important to distinguish between the motions of wave itself and the motion of the individual’s particles that make up the wave. Common example included the waves that propagate through a field of wheat. The individuals stalks sway back and forth as wave passes, but they do not change their location. Similarly, a ‘wave’ at a ball game may propagate around the stadium more quickly than a person can run, but the individual people making up the waves simply stand and sit in one place. From these example it clear that waves can come in a variety of types.
2.2 WAVES INTERFERENCE
Consider the wave pulses on the string. When they combine, the resulting pulse has amplitude equal to the sum of the amplitude of the individual pulses. This is referred to as constructive interference.
It is important to note that the wave do not simply disappear when they experience destructive interference. The wave pulses continue on unchanged after they interact. This make sense from an energy point of view, after all, each wave carries energy, hence the wave, along with their energy, cannot simply vanish. Therefore the energy of the wave is still present at this instant of time; it is just in the form of the kinetic energy.
It should also be noted that all waves exhibit an interference effect and not limited to waves on string. In fact, you should say that interference in one of the key characteristics that define wave. In general, when waves combine they form interference patterns that include region of both constructive and destructive interference. Note that regions of constructive interference separated by regions of destructive interference.
2.3 SUPERPOSITION
The combination of two or more waves to form a resultant wave is referred to as superposition. When waves are of small amplitude, they superposed in the simplest of ways they just add. For example, consider two waves on the string, describe by wave function y1 and y2, if these two waves are present on the string at the same time, the result is wave given by;
Y=y1+y2
To see how superposition works as a function of time, consider a string with two wave pulses on it. One travels in each direction. When the pulses arrive in the same time region, they add, as stated. The question is what do the pulse look like after they have passed through one another? Does their interaction change them in anyway? The answer is that waves.
2.4 ELECTROMAGNETIC WAVE
Electromagnetic waves are transverse wave. They have some electric properties and some magnetic properties. This wave consists a charging electric and magnetic field. An electric field is a region in which charged particle can pushed or pulled. Wherever there is an electric charge, there is an electric field associated with it. A magnetic field is a region in which magnetic forces are present. Both fields vibrate at the right angle to each other toward the wave direction. When the electric fields change, so does electric field to change. An Electromagnetic wave is the result of this two fields constantly each other to change. Electromagnetic waves travel as vibrations in electric and magnetic fields and do not need a medium.
Even electromagnetic radiations have some properties do not fit the wave model, but general the electromagnetic wave has properties as ordinary wave such reflection, diffraction, interference and able to transferred energy. The energy transferred by electromagnetic wave called electromagnetic radiations. The energy transferred by electromagnetic wave will increase to its amplitude and frequency.
Visible light is part of a large spectrum of energy that includes other familiar electromagnetic energy regions: microwaves, radio waves, Ultraviolet and X-rays all are form a continuous spectrum of light that we cannot see. The colours of rainbow form a continuous spectrum of light in the visible wavelength region as does the “light” in the other regions. Infrared light occurs at wavelengths just below red light, hence the name, infra- (below) red. Near- infrared is the “colour” of the heating coil on an electric stove just before it glows red. The thermal (of mid) infrared colours are found at even longer wavelengths.
2.5 WAVE PENOMENA
A black body is a material that is a perfect emitter of heat energy in that it emits all energy it absorbs and has an emissivity value of 1 at all temperatures and wavelengths. Anything that emits energy with Planck distribution can be called a blackbody. Effective emissivity of a cavity type blackbody will normally be much higher than the surface emissivity due to the multiple energy bounces inside the body cavity. In contrast a material with an emissivity value of 0 would result in readings of reflected energy only and not the actual material. For example, if an object had the potential to emit 100 units of energy but only emits 90 units in the real world. That object would have an emissivity value of 0.90. In the real world there are not perfect “blackbody” and very perfect infrared mirrors. So, most objects have an emissivity between 0 and 1.
A blackbody is an entity that absorbs all electromagnetic radiation falling upon it. As it is a perfect absorber, it neither reflects nor transmits. As with most of theoretical physics, this ideal entity does not exits. It can be closely approximated by a practical blackbody radiator. A good example is a hollow metal cylinder in the central isothermal region of the furnace. The cylinder (or radiator) will have a hole through which thermal radiation can escape. We can get nearer ideal blackbody conditions by oxidizing or blackening the interior walls of the radiator. We then have a practical standard source of thermal radiation, as described by the Planck equation, which can be used in measuring emissivity.
2.6 KIRCHOFF”S LAW
When an object is at thermal equilibrium, the amount of absorption will equal the amount of emission.
2.7 STEPHAN- BOLTZMANN LAW
Stefan – Boltzmann Law state,in an object were emit electromagnetic radiation for a perfect blackbody is The hotter an object becomes the more infrared energy it emits.
The law states that the emitted radiance is proportional to the temperature of the object. If an object is not a perfect blackbody, the law does not apply. Instead, a correction factors need to be added.
2.8 WIEN’S DISPLACEMENT LAW
The wavelength at which the maximum amount of the energy is emitted becomes shorter as the temperature increases.
2.9 PLANCK’S EQUATION
Planck’s equation describes the relationship between spectral emissivity, temperature and radiant energy.
Everything in nature emits electromagnetic radiation that is a function of its temperature, and not (in theory) a function of what it is made out of. That radiation is what we call thermal radiation. In the case of perfect black body, which absorbs 100% of all radiation that hits it, the thermal radiation emitted of the temperature only. Furthermore, no object will emit purely thermal radiation with more intensity than a true blackbody, so its emission is a maximum. In the case of real world stuff, what it is made out of does make a difference, and nature expresses that difference by sort of efficiency; some things will emit more thermal radiation, even though they are the same temperatures as something else. High emissivity material emits more thermal radiation, and low emissivity material emits less thermal radiation, at any given temperature. The electronic medicine and the sick man act as a black body. They have electromagnetic wave in infrared spectrum range, so this wave can used as a code and manipulate to produce medicine or to cure disease in a sick man.
