M1 Week 21 Jan 2025 Light - Google Slides PDF

Unit 6: Light Week 21 Topic: Reflection and Refraction  LEARNING OBJECTIVES Students will be able to: Describe how light is reflected from a plane mirror Understand the laws of reflection Draw ray diagrams to show reflection of light Understand what is refraction of light ...

Unit 6: Light Week 21 Topic: Reflection and Refraction  LEARNING OBJECTIVES Students will be able to: Describe how light is reflected from a plane mirror Understand the laws of reflection Draw ray diagrams to show reflection of light Understand what is refraction of light  Reflection of light We often see our reflections in mirror. John is looking in the flat mirror. He can see his reflection in the mirror. He notices few things about his reflection. It is the right way up, same size and the same colour as John. If he moves closer to the mirror the image moves closer and similarly if he moves away the image moves away as well. There is nothing behind the mirror that is why the image is virtual. The images that are projected on a screen are real images. The image is laterally inverted.  Laws of Reflection i- The angle of Incidence is always equal to the angle of Reflection. i =r ii- The incident ray, the reflected ray, and the normal to the surface of the mirror all lie in the same plane How to measure angle of incidence and reflection Making Measurement Making Measurement  REFRACTION OF LIGHT A pencil appears bent or broken when it is partially immersed in water. Why?  REFRACTION OF LIGHT When light travels from one transparent medium to another, such as from air to water, the light changes its direction. AIR WATER This bending of light is called refraction. The change of direction happens at the boundary, or interface, between the two media.  REFRACTION Angle of incidence: The angle between the normal and the incident ray reaching the boundary is called the angle of incidence Angle of refraction: The angle between the refracted ray and normal on the other side of the boundary is called the angle of refraction REFRACTION  REFRACTION (From air into water/glass) Light rays bend towards the normal when the rays travel from a less dense medium to a denser medium (eg: air to water, air to glass,)  REFRACTION (From water/glass into air ) If light goes from more dense medium to less dense medium like from water to air then the direction of ray will move away from the normal  WHY DOES REFRACTION HAPPEN In air, light travels about 300 000 km/s but in water it only travels about 230 000 km/s. So light going in from air into water slows down. Light coming out of water into the air speeds up. In both cases the direction will change. The speed changes in different materials depends on the density of the material A more dense material will slow down the light more, so the light will be refracted more as shown in diagrams  APPLICATION OF REFRACTION A spoon appears bent or broken when it is immersed in water as shown in the figure.  APPLICATION OF REFRACTION Refraction explains why a pool looks shallower than it actually is. Light is refracted off a rock at the bottom of he pool and travels to the surface. It changes direction when it travels into the air. When light reaches your eye, your brain assumes that its has travelled in a straight line. So you see the rock as being in a different place but in reality it has changed its direction. The depth that rock appears to be is called the apparent depth, which is shallower than the real depth.  APPLICATION OF REFRACTION The bent pencil isn’t really bent. The refraction of the light from the end of pencil at X makes it look as if the light is coming from Y SPEED OF LIGHT AND REFRACTION Speed of light changes when it passes from one medium to another The amount of speed change when light passes from one medium to another depends on the material The ratio of the two speeds is called the refractive index. SPEED OF LIGHT AND REFRACTION Refractive index does not have a unit because it is a ratio of two speeds. The speed of light slows down more in diamond than in glass because refractive index of diamond ( 2.4 ) is greater than the refractive index of glass (1.5). The refractive index is high if the light slows down a lot as in diamond.  Applications: A lens uses refraction to form an image of an object for various purposes, such as magnification spectacles worn by people with defective vision use the principle of refraction refraction is used in peepholes of house doors, cameras, movie projectors and telescopes  CONCEPT CHECK: QUESTION 1: QUESTION 2: QUESTION 3: The angle between. Swimming pools and the An example of changing ocean look shallower than they the incidence ray and mediums is when light really are due to: the normal is called goes from ______ to the _________. ______. A. reflection A. Ray of light B. Dispersion A. Air, wood B. Angle of incidence C. Refraction B. Air, water C. Angle of reflection D. total internal reflection C. Air, plastic  CONCEPT CHECK: QUESTION 4: QUESTION 5: QUESTION 6 Which statement about The speed changes in different refraction is true? Which of the following will slow materials depends on the _____ down the light more of the material. A. Light bends when it passes from one medium to another a) Glass a) Density B. Refraction is due to b) Diamond b) Acceleration changes in the wavelength of light waves c) Strength c) Water C. Charges within in a d) None of above d) None of above material can speed up light D. The speed of light does not depend on what medium it is traveling through  CONCEPT CHECK: Which letter in the diagram Which letter in the diagram Which letter in the diagram represents the refracted represents the angle of incidence? represents the angle of refraction? ray? 1. label D 1. label D 1. label D 2. label A 2. label C 2. label C 3. label C 3. label E 3. label E 4. label F 4. label A 4. label F