Chapter 5 Notes 'Ray Model of Light' Secondary One PDF

HILLGROVE SECONDARY SCHOOL SCIENCE DEPARTMENT SECONDARY ONE EXPRESS / NORMAL (ACADEMIC) CHAPTER 5: RAY MODEL OF LIGHT (Answers) Name: __________________________ Class: 1 – __...

HILLGROVE SECONDARY SCHOOL SCIENCE DEPARTMENT SECONDARY ONE EXPRESS / NORMAL (ACADEMIC) CHAPTER 5: RAY MODEL OF LIGHT (Answers) Name: __________________________ Class: 1 – ___ Date: ___________ By the end of this chapter, you should be able to: No. Learning outcomes Tick 1 Show an understanding that the ray model represents the path taken by light. 2 Describe the effects and uses of reflecting surfaces (e.g., plane and curved). 3 Explain how reflection is affected by a smooth and rough surface using the ray model of light. 4 *Show an understanding that the change in the speed of light in different mediums can cause refraction (calculation of angles not required). 5 *Describe some effects of refraction. 6 *Describe the dispersion of white light by a prism using the ray model of light. 7 Investigate the characteristics of the image formed by a plane mirror. 8 *Investigate that the angle of reflection is equal to the angle of incidence, with respect to the normal. 9 Show an awareness that EM radiation (e.g., infrared, ultraviolet and light) has both beneficial and harmful effects. 10 Show an awareness about the impact of light produced by technology, on society and environment (e.g., city lights can improve night visibility but cause light pollution, disorientation of birds and use up a lot of electrical energy). 1. How do we represent light? 1.1 What is light? Light is a form of energy that is produced by a light source. Examples of light sources: sun, light bulb, lamp, candle and fireflies. Light travels in a straight line from the light source into our eyes, allowing us to see the object. 1 1.2 The ray model of light The behaviour of light can be represented by a straight line in a ray diagram. o The straight line shows the path taken by the light. o The arrow shows the direction of light. [Refer to AB 5.1.1 (page 1-4)] 2. What is reflection and what are its applications? 2.1 How do we see objects that do not emit light? Most objects in our daily lives do not emit light on their own so we can only see them in the presence of a light source. Light from a light source can bounce off an object and enter our eyes. The bouncing of light off a surface is called reflection. Light travels in a straight line even when it bounces off a surface. 2.2 Characteristics of images formed by plane mirrors Upright Same size as the object Laterally inverted Virtual Distance between the image and the mirror is equal to the distance between the object and the mirror 2 2.3 Using the ray model of light to represent reflection The incident ray is the light ray hitting the reflecting surface. The reflected ray is the light ray travelling away from the reflecting surface after bouncing off the surface. The normal is the line perpendicular to the surface at the point of incidence. The angle of incidence (i) is the angle between the incident ray and the normal. The angle of reflection (r) is the angle between the reflected ray and the normal. The angle of incidence is equal to the angle of reflection (i.e., i = r). Checkpoint 1 Q1. The diagrams below show a ray of light being reflected by a plane mirror. State the angle of incidence and the angle of reflection. (a) (b) Angle of incidence = 30° Angle of incidence = 50° Angle of reflection = 30° Angle of reflection = 50° [Refer to AB 5.2.1 (page 5-12)] 3 2.4 Drawing ray diagrams for images formed by plane mirrors Step 1: Measure the perpendicular distance between the object and the mirror. Draw a dotted line to represent this distance. Step 2: Extend the dotted line into the mirror. Ensure that the distance between the image and the mirror is equal to the distance between the object and the mirror. Indicate the position of image using dotted lines. Step 3: Draw a line from the image to the eye. The line from the image to the mirror should be dotted to represent the virtual ray while the line from the mirror to the eye should be continuous to represent the reflected ray. Step 4: Draw a continuous line from the object to the mirror to represent the incident ray. Step 5: Draw arrows on the incident and reflected rays to show the direction of light. 4 Checkpoint 2 Q1. Complete the ray diagram below to show how the eye sees the image of object X in a plane mirror. [Homework: AB 5.2.2 (page 16-18)] 2.5 Types and uses of mirrors Type of mirror Plane Convex Concave Diagram Curved Curved Mirror surface Flat outwards inwards Virtual Virtual Virtual Upright Upright Upright Characteristics Same size as Diminished Magnified of image object Provides a formed wider field of vision To check our Blind corner Dental mirror appearance mirror at road Shaving or make To make a junctions up mirrors Uses periscope Rear-view and side mirrors of cars [Refer to AB 5.2.3 (page 19-22)] 5 3. Types of reflection Type of Regular Irregular reflection Ray diagram Type of surface Smooth Rough When parallel rays of light fall When parallel rays of light fall Effect on light on a smooth surface, each ray on a rough surface, each ray is rays is reflected in the same reflected in a different direction. direction. Image formed A clear image is formed. No image is formed. [Refer to AB 5.3.1 (page 23-24)] 4. What happens when light passes through different mediums? 4.1 Refraction of light Refraction is the bending of light when it travels from one medium to another of a different optical density. Refraction occurs due to the change in speed of light when it travels from one medium to another. 6  When a light ray travels from an optically less dense medium (e.g., air) to an optically denser medium (e.g., glass), it slows down and bends towards the normal. When a light ray travels from an optically denser medium (e.g., glass) to an optically less dense medium (e.g., air), it speeds up and bends away from the normal. Checkpoint 3 Q1. Complete the ray diagrams below to show the path of light as it travels from one medium to another. (a) (b) (c) (d) Q2. Complete the ray diagrams below to show the path of light as it travels into and out of a glass block. (a) (b) 7 4.2 Effects of refraction When a glass block is placed on this page, the bending of light will cause the words to appear closer to the glass surface than they actually are. When a straw is placed in a glass of water, the bending of light will cause the straw to appear closer to the water surface than it actually is and appear bent. The bending of light will cause swimming pools to appear shallower than they actually are. Hence, the apparent depth is less than the actual depth. Checkpoint 4 Q1. A boy drops a golf ball into a pool of water. (a) Complete the ray diagram below to show how the boy is able to see the image of the golf ball in a pool of water. (b) On the diagram above, label the apparent depth and actual depth. (c) Explain why the golf ball appears shallower than it actually is. As light travels from water into air, it speeds up and bends away from the normal. Thus, the apparent depth is less than the actual depth. 8 4.3 Dispersion of light When a ray of white light passes through a glass prism, it splits into seven colours: red, orange, yellow, green, blue, indigo and violet. This is because light rays of different colours bend towards the normal by different angles as they travel at different speeds. The splitting of white light into seven colours is known as dispersion. [Refer to AB 5.4.1 (page 25-30)] 5. What is the impact of applications of radiation on society and the environment? 5.1 Infrared radiation Application: o Used in thermal imaging cameras to screen people for fever. o Used in remote controls to send signals. Harmful effects: o Overexposure to infrared radiation can damage eyes. o Infrared radiation trapped in the atmosphere contributes to climate change. 5.2 Ultraviolet (UV) radiation Application: o Used to sterlise medical equipment, food and water. o Exposure to small amounts of UV radiation increases the production of vitamin D in our bodies. Harmful effects: o Overexposure to UV radiation can damage eyes and cause skin cancer. 9 5.3 Visible light Applications: o Enables us to see and carry out our daily activities. o Plants require light for photosynthesis. Harmful effects: o Causes light pollution which negatively impacts living things that depend on Earth’s cycle of day and night to carry out life-sustaining activities. E.g., disrupts the migration pattern of birds. E.g., affects our sleep cycle. o Uses a lot of electrical energy. [Refer to AB 5.5.1 (page 31-32)] [Homework: AB Practice Questions (page 33-35)] 10