Sci10 Q1M2 PPT 1 Nature of Light 2 PDF

 The electromagnetic spectrum consists of different types of waves called electromagnetic waves or radiations. Each type occupies a particular range of wavelengths. The EM waves have common properties: ⚬ They carry energy from one place to another. ⚬ They do not need a medium to...

 The electromagnetic spectrum consists of different types of waves called electromagnetic waves or radiations. Each type occupies a particular range of wavelengths. The EM waves have common properties: ⚬ They carry energy from one place to another. ⚬ They do not need a medium to travel. ⚬ They can travel in a vacuum at a speed of 3×10^8 m⁄s. ⚬ They obey the wave equation v = f x λ ⚬ They are transverse waves. Learners should be able to: Explain the different properties of light Describe the nature of images (L-O-S-T) formed by plane and spherical mirrors; Describe the nature of images (L-O-S-T) formed by concave and convex lenses; What is light? is light a particle or a wave?  Light has been studied extensively but its fundamental nature is still a mystery. Corpuscular theory of light ⚬ Light is made up of streams of particles (corpuscles). Wave theory of light. ⚬ He proposed that under some Christian Huygens Isaac Newton circumstances, light does spread out.  Newton rejected Huygens’ idea and according to him, light travels only in a straight lines (diffraction had not yet been discovered) which explains why shadow is formed when an object is placed in a beam of light. Christian Huygens Isaac Newton  In 1801, Thomas Young (1773-1829) discovered diffraction and interference of light which can be explained only in terms of wave theory. Christian Huygens Isaac Newton  Maxwell asserted that light is a form of high frequency electromagnetic wave. It was later proven by Hertz in 1887 by producing and detecting electromagnetic waves. However, he also discovered Photoelectric effect which Wave?? Particle?? contradicted the wave theory.  Einstein’s quantization model assumes that the energy of a light wave is present in particles called photons; where the energy of a photon is proportional to the frequency of the electromagnetic wave shown by the equation: E = hf  Arthur Compton’s (1892-1962) experiment in 1923 showed that photons of X-rays decreased in energy when colliding with electrons. This suggested that radiation, including light, behaves as particle.  A year later, Louis-Victor de Broglie (1892-1987) extended the possibility further by proposing that matter can have a wave properties and thus reinforced the fact that light, and even matter, has a dual nature.  Effects of Materials on Light Reflection Diffraction Refraction Interference Total Internal Reflection Rayleigh Scattering Dispersion Polarization Travels in a straight line Travels very fast  Materials can be classified based on how it responds to light incident on them: Transparent materials – allow light to easily pass through them Translucent materials – allow light to pass through but distorts the light during the passage Opaque materials – absorb light  Reflection happens when a wave hits a surface which it cannot pass, then it bounces back.  The incident, reflected, and refracted rays and the normal to the surface all lie on the same plane The angle of reflection is equal to the angle of incidence for all wavelengths and for any pair of materials  Types of Reflection 1. Diffuse Reflection 2. Specular Reflection Refraction is the bending of a wave caused by a change in its speed as it moves from one medium to another. 3 x 10^8 m/s  Rule of thumb in refraction If light slows down, or moves from a lower index of refraction to a higher index of refraction, it will refract towards the normal line. If light speeds up, or moves from a higher index of refraction to a lower index of refraction, it will refract away from the normal line. Seatwork Points Questions 1. The man wishes to kill the fish using a spear, should he aim the spear above, below, or directly at the observed fish to make a direct hit? 2. The man wishes to "spear" a fish with a laser, should he aim the laser beam above, below, or directly at the observed fish to make a direct hit? Law of Refraction The ratios of the sines of angles θa and θb, where both angles are measured from the normal to the surface is equal to the inverse ratio of the two indices of refraction: Sample Problem 1: Sample Problem 2: Calculate the index of refraction for medium B. Sample Problem 3: Light travels from air into an optical fiber with an index of refraction of 1.44. In which direction does the light bend? If the angle of incidence on the end of the fiber is 22 degrees, what is the angle of refraction inside the fiber? Sketch the path of light as it changes media. Real Life Applications: Mirage A mirage is an apparent shift in the position of objects caused by refraction of light in different densities. During hot days, the layer of air is in contact with the ground and its molecules are farther apart. Hence, light travels faster through hot air, causing light rays near the ground to bend upward. This makes the image appear upside down, as if it were reflected from a surface of water. The inside surface of water, glass, or other transparent materials can act like a perfect mirror.  When light travels from a denser to a less dense medium and strikes the surface at an angle greater than the critical angle (the least angle of incidence) of a material, the light beam is not able to get out of the denser material. All light will be reflected internally and the effect is called total internal reflection. Real Life Examples The process by which light is separated into its colors due to differences in degrees of refraction is called, dispersion. Seatwork Points Questions How do rainbows form? Seatwork Points Questions How are rainbows formed? Spreading out of light when passing through a small slits or around sharp edges or corners is called diffraction. Spreading out of light when passing through a small slits or around sharp edges or corners is called diffraction.  When two light waves meet or coincide, it can create either constructive or destructive interference based on how the crests & troughs of the waves meet.  Light travels in straight lines This phenomenon is called Rayleigh as long as nothing disturbs it. Scattering. As light moves through the atmosphere, it bumps into bits of solid particles or gas molecules and become scattered in all directions by either reflection or refraction. Seatwork Points Questions Why is the sky blue? Why is the sky blue? As light moves through the atmosphere, most of the longer wavelengths pass straight through. However, much of the shorter wavelengths, like blue, interact with the gas molecules and become scattered through the atmosphere. Seatwork Points Questions Why are sunsets/sunrise red?  Why are sunsets/sunrise red? At sunset or sunrise when the sun is near the horizon or low in the sky, sunlight travels a longer distance through the atmosphere before it gets to your eyes.  This is the process of transforming unpolarized light (waves vibrating at all directions) into a polarized light (waves are regulated and vibrating in one direction).  This is the process of transforming unpolarized light (waves vibrating at all directions) into a polarized light (waves are regulated and vibrating in one direction).