assignment # 5..physics..after midz

8/8/2019 Assignment # 5..Physics..After Midz

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Q # 1(a)

Reflection:

Reflection is the change in direction of a wavefront at an interface between twodifferent media so that the wavefront returns into the medium from which it originated. Commonexamples include the reflection of light , sound and water waves . The law of reflection says thatfor specular reflection the angle at which the wave is incident on the surface equals the angle atwhich it is reflected. Mirrors exhibit specular reflection.

Refraction:

Refraction is the change in direction of a wave due to a change in its speed . This ismost commonly observed when a wave passes from one medium to another at any angle other than 90 or 0. Refraction of light is the most commonly observed phenomenon, but any type of wave can refract when it interacts with a medium, for example when sound waves pass fromone medium into another or when water waves move into water of a different depth.

Total internal Reflection:

Total internal reflection is an optical phenomenon that happens when a rayof light strikes a medium boundary at an angle larger than a particular critical angle with respect tothe normal to the surface. If the refractive index is lower on the other side of the boundary, no light canpass through and all of the light is reflected . The critical angle is the angle of incidence above which thetotal internal reflection occurs.

Dual nature of light:

Physics experiments over the past hundred years or so havedemonstrated that light has a dual nature. In many instances, it is convenient to representlight as a "particle" phenomenon, thinking of light as discrete "packets" of energy that wecall photons . Now in this way of thinking, not all photons are created equal, at least in termsof how much energy they contain. Each photon of X-ray light contains a lot of energy incomparison with, say, an optical or radio photon.

The other way of representing light is as a wave phenomenon. This is somewhat moredifficult for most people to understand, but perhaps an analogy with sound waves will beuseful. When you play a high note and a low note on the piano, they both produce sound,but the main thing that is different between the two notes is the frequency of the vibratingstring producing the sound waves--the faster the vibration the higher the pitch of the note.If we now shift our focus to the sound waves themselves instead of the vibrating string, wewould find that the higher pitched notes have shorter wavelengths , or distances betweeneach successive wave.


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Q#2

Coherence of light:

For many photonic applications it is desirable to have a "monochromatic"(ideal) point light source. An ideal light source would emit only one exact

frequency f 0 and its physical size would be infinitely small (an ideal pointsource). Such a source cannot exist in reality. Every real source of light has

some emission uncertainty which appears as linewidth ( f. Also, every real lightsource has some (non-zero) physical size. Coherence is a concept that thatestablishes the limits within which a real light source can be considered ideal.

here are two types of coherence:

(1) Temporal Coherence (related to the emitted linewidth)

(2) Spatial Coherence (related to the physical size of the source).

P olarisation of light:

P olarization (also p olarisation ) is a property of certain types of waves that describes the orientation of their oscillations . Electromagnetic waves , such as light , and gravitational waves exhibit polarization;acoustic waves ( sound waves) in a gas or liquid do not have polarization because the direction of vibration and direction of propagation are the same. By convention, the polarization of light is describedby specifying the orientation of the wave's electric field at a point in space over one period of theoscillation.

Why colour of sky is blue?

L ight is a kind of energy that can travel through space. L ight from the sun or a light bulb lookswhite, but it is really a mixture of many colors. The colors in white light are red, orange,yellow, green, blue and violet. You can see these colors when you look at a rainbow in the sky.

The sky is filled with air. Air is a mixture of tiny gas molecules and small bits of solid stuff, likedust.

As sunlight goes through the air, it bumps into the molecules and dust. When light hits a gasmolecule, it may bounce off in a different direction. Some colors of light, like red and orange,pass straight through the air. But most of the blue light bounces off in all directions. In thisway, the blue light gets scattered all around the sky.


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When you look up, some of this blue light reaches your eyes from all over the sky. Since you seeblue light from everywhere overhead, the sky looks blue.

How sun glasses work

Normal sunglasses work by blocking out some of the light in one of two ways. Most of them arereally just colored filters: they let through only light of a certain color (the color of the lens) and block out the rest. Since only a fraction of the light gets through, you see a darkened (and colored) picture. The other type of sunglasses usepolarisation. Light travels in a wave motiona bit like the waves on the sea. But where ocean waves vibrate only up and down, light waveswriggle in every direction

Diffraction of light:

, the diffraction phenomenon is described as the apparent bending of waves around small obstacles andthe spreading out of waves past small openings. Similar effects occur when light waves travel through amedium with a varying refractive index or a sound wave through one with varying acoustic impedance .Diffraction occurs with all waves, including sound waves, water waves, and electromagnetic waves suchas visible light , x-rays and radio waves . As physical objects have wave-like properties (at the atomiclevel), diffraction also occurs with matter and can be studied according to the principles of quantummechanics .

Constructive and distructive interference: TYPES OF INTERFERENCE www.citycollegiate.com

...... There are two types of interference.

Constructive interference.

Destructive interference. CONSTRUCTIVE INTERFERENCE

When two light waves superpose with each other in such away that the crest of one wavefalls on the crest of the second wave, and trough of one wave falls on the trough of thesecond wave, then the resultant wave has larger amplitude and it is called constructiveinterference.

Distructive interference :When two light waves superpose with each other in such away that the crest of onewave coincides the trough of the second wave, then the amplitude of resultantwave becomes zero and it is called destructive interference.

What is a polarizer? When two light waves superpose with each other in such away that the crest of one wave

coincides the trough of the second wave, then the amplitude of resultant wave becomeszero and it is called destructive interference.

A p olarizer is a device that converts a beam of electromagnetic waves (light ) of undefined or mixed polarization into a beam with well-defined polarization. The common types of polarizers are linear polarizers and circular polarizers . Polarizers are used in many optical techniques and instruments ,


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and polarizing filters find applications in photography and liquid crystal display technology.

assignment # 5..physics..after midz

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