TEACHING POINT 1.Review the echo method.[ 10 min] 2.Identify luminous and non- luminous objects.[5 min] 3. Properties of light.[20min] What words are inscribed below 1.H T I L G 2. L E T C R F E 3. NSU 4. L O S U M I S U N 5. W A B N I OW 6. I R M ROR SPEED OF SOUND BY ECHO METHOD If a sound pulse takes 2 seconds to travel to the seafloor and return to the ship, what is the depth to the seafloor? (Use 1500 m/s as the speed of sound in water). A sound signal from the sonar on a ship is sent underwater into the sea. It takes 1.35 s for the signal to return to the ship. If sound travels at 1500 m/s, how deep is the sea? A group of students measured the time taken between seeing and hearing another student, 250 m away, clashing two pieces of wood together. They obtained the following timings in seconds: 0.73, 0.78, 0.69, 0.81, Use their measurements to obtain a speed of sound estimate. A thunderclap is heard 12 seconds after a lightning flash. Calculate the distance to the lightning flash. Take the speed of sound = 340 m/s What is light: Light is a form of energy that can be detected by our eyes. Luminous objects: Objects that produce their own light e.g candles,bulbs,sun, stars, glowings insects, etc Non-luminous objects: Objects which do not produce their light. They reflect the light that falls on them. E.g human beings,animals, plants, moon, tables,plants etc. Properties of (white) Light 1.Consits of seven colours. Red Orange Yellow Green Blue Indigo Violet 2. Light travels in a straight line. 3. Light is a transverse wave. 4. Light travels at 3 x 10 8 m/s. 5. Light reflects from objects. 6. Light undergoes refraction. 7. Light can be diffracted. TEACHING POINT 1.Demonstrate that light travels in a straight line.[ 2min] 2.Demonsrate reflection of light [5 min] 3. Properties of light.[20min] Identify these equipments A B C D E F G What is common to all these equipments? Properties of Light Properties of Light Light travels in straight lines: Laser when all the cards lie on a line, the observer will see light when middle card is moved, the observer will see darkness. Light cannot bend. Light travels VERY FAST around 300,000,000 M/S Light takes 8 minutes reach us from the sun. How far is the sun? Shadows Shadows are places where light is blocked: Rays of light We see things because they reflect light into our eyes: Homework Reflection is bouncing back of light when it strikes an object. CC A B Plain Mirror Incoming Light Reflection Where will the light ray finish? D B C B A Plain Mirror Incoming Light Reflection Where will the light ray finish? A B C A Plain Mirror Incoming Light Reflection Where will the light ray finish? A B C B Plain Mirror Incoming Light Reflection Where will the light ray finish? TEACHING POINT 1.Students to attempt Revision exercise 1 [ 20min] 2.State and apply laws of reflection [15 min] 3. Describe images formed by a plane mirror.[10min] YEAR 10 TEST 1 TERM 2 SOLUTIONS Q. ANS Q 1 D 9D 2 B 10B 3 B 11C 4 D 12B 5 A 13A 6 C 14A 7 A 15C 8 B 16C Reflection from a mirror: Incident ray Normal Reflected ray Angle of incidence Angle of reflection Mirror The Laws of Reflection 1. Angle of incidence = Angle of reflection 2. The incident ray, reflected ray and the normal all lie on the same plane (same side of the mirror) i=r Plain Mirror 70 0 Find the angle of reflection Plain Mirror 40 0 Find (a)Angle of incident. (b) angle of reflection Normal Properties/characteristics of image formed by plane mirror 1.The image is same size as the object. 2.The image is same distance behind the mirror as the object. 3.The image is laterally inverted. 4.The image is virtual. LATERALLY INVERTED Same distance, same size BC= CD Same distance from the mirror Same size (height) H object =h image Using mirrors Two examples: 1) A periscope 2) A car headlight ABC A Glass Block Incoming Light D Refraction Where will the light ray finish? A B C B Glass Block Incoming Light D Refraction Where will the light ray finish? A B C B Glass Block Incoming Light D Refraction Where will the light ray finish? A B CC Glass Block Incoming Light D Refraction Where will the light ray finish? Clear vs. Diffuse Reflection Smooth, shiny surfaces have a clear reflection: Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions Colour White light is not a single colour; it is made up of a mixture of the seven colours of the rainbow. We can demonstrate this by splitting white light with a prism: This is how rainbows are formed: sunlight is split up by raindrops. The colours of the rainbow: Red Orange Yellow Green Blue Indigo Violet Adding colours White light can be split up to make separate colours. These colours can be added together again. The primary colours of light are red, blue and green: Adding blue and red makes magenta (purple) Adding blue and green makes cyan (light blue) Adding all three makes white again Adding red and green makes yellow Seeing colour The colour an object appears depends on the colours of light it reflects. For example, a red book only reflects red light: White light Only red light is reflected A white hat would reflect all seven colours: A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue): Purple light White light Using coloured light If we look at a coloured object in coloured light we see something different. For example, consider a football kit: White light Shorts look blue Shirt looks red In different colours of light this kit would look different: Red light Shirt looks red Shorts look black Blue light Shirt looks black Shorts look blue Some further examples: ObjectColour of light Colour object seems to be Red socks Red BlueBlack GreenBlack Blue teddy RedBlack Blue Green Green camel Red Blue Green Magenta book Red Blue Green Using filters Filters can be used to block out different colours of light: Red Filter Magenta Filter Investigating filters Colour of filterColours that could be seen Red Green Blue Cyan Magenta Yellow Red Magenta White Yellow BlueGreen Cyan Refraction Refraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. When a pen is placed in water it looks like this: In this case the light rays are slowed down by the water and are _____, causing the pen to look odd. The two mediums in this example are ______ and _______. Words speed up, water, air, bent