Reflection and Refraction of Light Grade 10 Lesson 4.1 PDF

REFLECTION AND REFRACTION OF LIGHT Grade 10 - Lesson 4.1 Sir Gil Joshua M. Laurencio  LESSON OBJECTIVES Discuss the different properties of light, Identify ways in which these properties of light are put to practical use, Compare and contrast reflection and refraction of light, D...

REFLECTION AND REFRACTION OF LIGHT Grade 10 - Lesson 4.1 Sir Gil Joshua M. Laurencio  LESSON OBJECTIVES Discuss the different properties of light, Identify ways in which these properties of light are put to practical use, Compare and contrast reflection and refraction of light, Define the index of refraction; and Explain Snell’s Law and how it is used to predict refraction of light.  LIGHT SOURCE Light is electromagnetic Natural radiation that has Sun, Stars, Fire, properties of waves and Bioluminescence, particles. and lightning. Light travels in straight Man-made lines called rays. Light bulbs, lamps, The bundle of light rays flashlight, candle, are called beam. and lasers. Reflection occurs when REFLECTION light waves strike a surface and bounce back. Reflection happens because light cannot pass through certain materials, so it bounces back instead. Everything we see reflects light. This is how we are able to see objects. TWO KINDS OF REFLECTION  SPECULAR REFLECTION Also called Regular Reflection. This occurs when light hits a smooth, shiny surface, like a mirror or calm water. The light rays bounce off in a well-organized, uniform direction. As a result, you can see a clear reflection or image. Example: A mirror reflects light in a way that allows you to see your face clearly. SPECULAR REFLECTION  DIFFUSE REFLECTION This happens when light hits a rough or uneven surface, like paper or a wall. The light rays scatter in many directions because the surface is bumpy at a microscopic level. You don't see a clear reflection but can see the object itself because the light spreads evenly. Example: A wall reflects light diffusely, so you can see the wall, but not a reflection of yourself. DIFFUSE REFLECTION SPECULAR VS DIFFUSE Specular reflection gives clear reflections, while Diffuse reflection scatters light and gives no clear image but lets you see the object. ABSORPTION AND SCATTERING OF LIGHT Reflection of light may also exhibit “Absorption and Scattering” Absorption is the transfer of energy carried by the light waves to the particles of matter; while Scattering is when light bounces off tiny particles (like dust, air molecules, or water droplets) and is redirected in different directions. Absorption Scattering  LAW OF REFLECTION OF LIGHT 1. The incident ray, the normal to the mirror at the point of incidence, and the reflected ray all lie in the same plane. LAW OF REFLECTION OF LIGHT  LAW OF REFLECTION OF LIGHT 2. The angle of incidence (the angle between the incident ray and the normal, an imaginary line perpendicular to the surface) is equal to the angle of reflection (the angle between the reflected ray and the normal). In simple terms: The angle at which light hits a surface is the same angle at which it reflects off.  NORMAL INCIDENT RAY REFLECTED RAY i r MIRRORS AND ANGLE OF INCIDENCE ANGLE OF REFLECTION REFLECTION PLANE MIRROR LAW OF REFLECTION i = r LAW OF REFLECTION OF LIGHT These laws of reflection are applicable to all types of reflecting surfaces, including plane mirrors and spherical surfaces. LEARNING CHECK The diagram shows a light ray hitting a plane mirror. What would be the angles of incidence and reflection? A i = 30°, r = 30° B i = 60°, r = 30° C i = 30°, r = 60° 30° D i = 60°, r = 60°  LEARNING CHECK The correct answer is D. The angle of incidence and angle of reflection is 60°. D ANSWER KEY i = 90° - 30° = 60° 60° 60° Since i = r, then the angle of reflection (r) is 30° also 60°. Refraction is the bending of REFRACTION light as it passes from one medium to another. This happens because light changes speed when it moves between different materials. e.g. putting a pencil in a glass of water.  REFRACTION When light slows down (e.g., moving from air to water), it bends toward the normal (an imaginary line perpendicular to the surface). When light speeds up (e.g., moving from water to air), it bends away from the normal. REFRACTION Dispersion is the effect associated with the separation of light into DISPERSION colors by a prism. As light passes through the prism, its components are refracted at different angles because of their different wavelength. Red light bent the least, while violet bent the most. INDEX OF REFRACTION The index of refraction is a measure of how much light slows down and bends when it passes from one medium (like air) into another medium (like water or glass) The refractive index (n) is calculated by dividing the speed of light in a vacuum (c) by the speed of light in the material (v) INDEX OF REFRACTION Problem 1 Light travels through a specific material with a refractive index of 1.5. If the speed of light in a vacuum is 3.00×10^8 m/s, find the speed of light in this material.  INDEX OF REFRACTION Problem 2 Light travels from air into a medium where its speed is measured to be 2.25×10^8 m/s. What is the index of refraction of the medium? INDICES OF REFRACTION OF LIGHT PAGE 148 REFRACTION As an incident ray passes through different media, the resulting rays bend. Two angles are formed, called the angle of incidence and the angle of refraction. The angle of refraction increases as the angle of incidence increases. When light moves from one medium to another, its speed and wavelength change, but its frequency remains the same.  REFRACTION When the angle of incidence produces an angle of refraction equal to 90 degrees in the medium, the angle is known as the critical angle. Total internal reflection is the phenomenon wherein the incident rays striking the boundary of two media are reflected back into the first medium and the bounding surface acts like a perfect reflector. REFRACTION  LAW OF REFRACTION OF LIGHT The incident ray, the reflected ray, and the normal to the interface of two transparent media at the point of incidence all lie in the same plane. LAW OF REFRACTION OF LIGHT(2ND) The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for the light of a given color and for the given pair of media. LAW OF REFRACTION OF LIGHT(2ND) LAW OF REFRACTION OF LIGHT(2ND) For example, if light goes from air (where n≈1 ) into water (where n≈1.33), the constant will be about 1.33 for that specific pair (air to water) and color of light. SNELLS LAW OF REFRACTION OF LIGHT Snell's Law describes how light bends (or refracts) when it passes from one medium to another. It provides a mathematical relationship between the angles of incidence and refraction and the refractive indices of the two media. EXAMPLE PROBLEM (1) A beam of light moves from air (with a refractive index of n1=1.00) into water (with a refractive index of n2=1.33). If the light hits the water surface at an angle of 45° from the normal, what is the angle of refraction in the water? EXAMPLE PROBLEM (STEPS) 1. Start with Snell’s Law 2. Derive the formula 3. Substitute the value 4. Solve for sin (θ2) 5. Find θ2 by taking the inverse sine: (Sin -1) 6. The Final answer should be 32.1∘  EXAMPLE PROBLEM (2) A ray of light of 500 nm wavelength in air impinges on a piece on a piece of crown glass at an angle of incidence of 35 degrees. Find the, a. Angle of Refraction b. Speed of light in the glass c. wavelength of light in the glass THANK YOU FOR LISTENING! Any questions?