Nature of Light - Part I (Fall 2024-2025) PDF

Faculty of Applied Health Science 10/20/2024 Technology 2024 Dr. Ahmed Yassin Physics The nature of light...

Faculty of Applied Health Science 10/20/2024 Technology 2024 Dr. Ahmed Yassin Physics The nature of light by Dr. Ahmed Yassin Fall 2024/2025 Topics  What is light ?  The field of Optics.  The dual nature of light.  Reflection.  Refraction. Dr./ Ahmed Yassin..... Physics Physics ‐ Dr. Ahmed Yassin 1 Faculty of Applied Health Science 10/20/2024 Technology 2024 Dr. Ahmed Yassin What is light ?  Light is a transverse, electromagnetic wave that can be seen by the typical human.  Like all electromagnetic waves, light can travel through a vacuum. Dr./ Ahmed Yassin..... Physics  The speed of light = 3 × 108 m/s.  From a biological standpoint, light is energy that activates the human eye and brain. It is the combination of the brain, eye and light that provides sight.  In physics, there are two theories by which light can be defined: the first theory defines light as particles and the second theory as waves. Dr./ Ahmed Yassin..... Physics Physics ‐ Dr. Ahmed Yassin 2 Faculty of Applied Health Science 10/20/2024 Technology 2024 Dr. Ahmed Yassin  Light can only be seen when looking either directly at a luminous object, such as a lamp, or when looking at illuminated objects which reflect light from a source.  Light exhibits properties such as; reflection, refraction, diffraction and interference. Dr./ Ahmed Yassin..... Physics The field of Optics Dr./ Ahmed Yassin..... Physics is the science that study of light and its interaction with matter, where ……..  allows us to understand the nature of colors.  facilitates to design optical devices such as; microscopes, telescopes, lenses, cameras, ……...  make a development in some applications such as; laser, optical fibers,...... Physics ‐ Dr. Ahmed Yassin 3 Faculty of Applied Health Science 10/20/2024 Technology 2024 Dr. Ahmed Yassin The dual nature of light Dr./ Ahmed Yassin..... Physics  Dual nature of light means light has two different nature, sometimes it behaves like a particle sometimes it behaves like a wave.  Particle theory (Corpuscular theory of light)  Isaac Newton stated in his Hypothesis of Light of 1675 that light was composed of corpuscles (tiny particles of matter) which were emitted in all straight directions from a source.  These tiny particles is called photons. The dual nature of light Dr./ Ahmed Yassin..... Physics  Wave theory  Christiaan Huygens (1629–1695) proposed that light was emitted in all directions as a series of waves in a medium called the Luminiferous ether. Physics ‐ Dr. Ahmed Yassin 4 Faculty of Applied Health Science 10/20/2024 Technology 2024 Dr. Ahmed Yassin The dual nature of light Dr./ Ahmed Yassin..... Physics  Electromagnetic theory  James Clerk Maxwell (1862) discovered that self- propagating electromagnetic waves would travel through space at a constant speed, which is equal to the previously measured speed of light.  From this, Maxwell concluded that light was a form of electromagnetic radiation.  Quantum theory  In 1900 Max Planck, suggested that although light was a wave, these waves could gain or lose energy only in finite amounts related to their frequency.  Physicists have noted that electromagnetic radiation tends to behave more like a classical wave at lower frequencies, but more like a classical particle at higher frequencies, but never completely loses all qualities of one or the other. Dr./ Ahmed Yassin..... Physics Physics ‐ Dr. Ahmed Yassin 5 Faculty of Applied Health Science 10/20/2024 Technology 2024 Dr. Ahmed Yassin Reflection The change in direction of a wavefront at an interface between two different media, where the reflected ray returns into the medium from which it originated. Dr./ Ahmed Yassin..... Physics Laws of Reflection  The incident ray, the reflected ray and the normal all lie in the same plane.  The angle of incidence = Angle of reflection. Dr./ Ahmed Yassin..... Physics Physics ‐ Dr. Ahmed Yassin 6 Faculty of Applied Health Science 10/20/2024 Technology 2024 Dr. Ahmed Yassin Types of Reflection of Light 1. Regular/ Specular Reflection  It refers to a clear and sharp reflection, like the ones you get in a mirror.  This reflective surface reflects almost all the light incident on it uniformly. Dr./ Ahmed Yassin..... Physics Types of Reflection of Light 2. Diffused Reflection  Reflective surface other than mirrors, in general, has a very rough finish. This may be due to wear and tear such as scratches and dents or dirt on the surface.  This type of reflection is what enables us to see non-shiny objects. Dr./ Ahmed Yassin..... Physics Physics ‐ Dr. Ahmed Yassin 7 Faculty of Applied Health Science 10/20/2024 Technology 2024 Dr. Ahmed Yassin 3. Multiple Reflection  A single image is formed when an object is placed in front of a mirror. What happens if we use two mirrors?  Since reflective surfaces such as mirrors are very good at preserving the intensity of light in a reflection, a single source of light can be reflected multiple times. This multiple reflection is possible Dr./ Ahmed Yassin..... Physics until the intensity of light becomes low. 3. Multiple Reflection  The variation of the number of images of an object placed between two mirrors with the angle between the mirrors can be described by a simple formula: 𝟑𝟔𝟎° 𝑵𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝒊𝒎𝒂𝒈𝒆𝒔 𝟏 𝒂𝒏𝒈𝒍𝒆 𝒃𝒆𝒕𝒘𝒆𝒆𝒏 𝒎𝒊𝒓𝒓𝒐𝒓𝒔 Dr./ Ahmed Yassin..... Physics  As we go on decreasing the angle between the mirrors, the number of images goes on increasing. Physics ‐ Dr. Ahmed Yassin 8 Faculty of Applied Health Science 10/20/2024 Technology 2024 Dr. Ahmed Yassin Some definitions of reflection  The angle of incidence: is the angle between incident ray on a surface and the line perpendicular to the surface at the point of incidence, called the normal. Dr./ Ahmed Yassin..... Physics 3  The angle of reflection: is the angle between a reflected ray and the normal drawn at the point of incidence to a reflecting surface. Refraction  is the change in direction of a wave passing from one medium to another. Dr./ Ahmed Yassin..... Physics  The bending of a wave when it enters a medium where its speed is different. Physics ‐ Dr. Ahmed Yassin 9 Faculty of Applied Health Science 10/20/2024 Technology 2024 Dr. Ahmed Yassin Refractive Index of a material Dr./ Ahmed Yassin..... Physics  The ratio between the speed of light in vacuum and the speed in the material. 𝑪 𝒏 𝑽  The wave speed is inversely proportional to the index of refraction.  The greater the index of refraction in a material, the slower the wave speed in that material. Snell’s Law Dr./ Ahmed Yassin..... Physics  Snell's law is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different media, such as water, glass, or air. 𝒏𝟏 𝒔𝒊𝒏𝜽𝟏 𝒏𝟐 𝒔𝒊𝒏𝜽𝟐 𝒏𝟏 𝒔𝒊𝒏𝜽𝟐 𝒗𝟐 𝟐 𝒏𝟐 𝒔𝒊𝒏𝜽𝟏 𝒗𝟏 𝟏 Physics ‐ Dr. Ahmed Yassin 10 Faculty of Applied Health Science 10/20/2024 Technology 2024 Dr. Ahmed Yassin Snell’s Law  If n1 > n2 , the beam bends away from the normal.  If n1 < n2 , the beam bends towards the normal.  If the beam is incident perpendicularly, it goes unrefracted. n1 < n2 n1 > n2 Dr./ Ahmed Yassin..... Physics Example (1): Dr./ Ahmed Yassin..... Physics  Calculate the incidence angle for the interface between water (n1 = 1. 33) and air (n2 = 1), where refractive angle = 𝟗𝟎𝒐 ? 𝒏𝟏 𝒔𝒊𝒏𝜽𝟏 𝒏𝟐 𝒔𝒊𝒏𝜽𝟐 𝒏𝟏 𝒔𝒊𝒏𝜽𝟏 𝒏𝟐 𝒔𝒊𝒏 𝟗𝟎𝒐 (1.33) 𝒔𝒊𝒏𝜽𝟏 𝟏 𝒔𝒊𝒏 𝟗𝟎° 𝜽𝟏 𝟒𝟖. 𝟔°. Physics ‐ Dr. Ahmed Yassin 11 Faculty of Applied Health Science 10/20/2024 Technology 2024 Dr. Ahmed Yassin Wave Optics  The wave nature of light is needed to explain various phenomena such as;  Interference.  Diffraction.  Polarization. Dr./ Ahmed Yassin..... Physics Interference Dr./ Ahmed Yassin..... Physics  Light waves interfere with each other much like mechanical waves do.  Interference occurs when the electric and magnetic fields of two or more light waves interact.  The electric and magnetic fields of the two waves add together to give you a new wave. Physics ‐ Dr. Ahmed Yassin 12 Faculty of Applied Health Science 10/20/2024 Technology 2024 Dr. Ahmed Yassin Conditions for Interference  For sustained interference between two sources of light to be observed, there are Dr./ Ahmed Yassin..... Physics two conditions which must be met: 1) The sources must be coherent, i. e., they must maintain a constant phase with respect to each other. 2) The waves must have identical wavelengths Dr./ Ahmed Yassin..... Physics Coherent sources  Two sources are said to be coherent if they emit light waves of the same frequency, amplitude and are always in phase with each other. Physics ‐ Dr. Ahmed Yassin 13 Faculty of Applied Health Science 10/20/2024 Technology 2024 Dr. Ahmed Yassin Producing Coherent Sources Dr./ Ahmed Yassin..... Physics  Light from a monochromatic source is allowed to pass through a narrow slit.  The light from the single slit is allowed to fall on a screen containing two narrow slits.  Recently, laser is commonly used as a coherent source.  The laser produces an intense, coherent, monochromatic beam, which can be used to illuminate multiple slits directly. Constructive interference Dr./ Ahmed Yassin..... Physics  When two light waves collide peak-to-peak and trough-to-trough.  The resulting light wave is stronger than either of its two components. Physics ‐ Dr. Ahmed Yassin 14 Faculty of Applied Health Science 10/20/2024 Technology 2024 Dr. Ahmed Yassin Destructive interference Dr./ Ahmed Yassin..... Physics  The waves are meeting peak-to-trough and trough-to-peak.  The two waves cancel each other out.  They are opposites of each other, and when they meet, the result is Zero. Young’s Double Slit Experiment  Thomas Young first demonstrated interference in light waves from two sources in 1801.  Light is incident on a screen with a narrow slit, So  The light waves emerging from this slit Dr./ Ahmed Yassin..... Physics 3 arrive at a second screen that contains two narrow, parallel slits, S1 and S2. Physics ‐ Dr. Ahmed Yassin 15