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© Boardworks Ltd 2003 KS4 Waves : Reflection
© Boardworks Ltd 2003 Objectives Recall that light travels in straight lines. Draw accurate ray diagrams. Describe how we see objects. Define the words opaque and transparent. Describe the images formed in a plane mirror. Recall how the angle of incidence and angle of reflection are related for a plane mirror. Describe the differences between convex and concave mirrors.
© Boardworks Ltd 2003 Light rays A light ray is a narrow beam of light. When drawing light diagrams always….. 1. Use a ruler. 2. Add an arrow to show the direction the light ray is travelling in.
© Boardworks Ltd 2003 How does light travel? 1)Fill a clear glass trough or empty fish tank with smoke. 2)Shine rays of light through the tank and describe what you see.
© Boardworks Ltd 2003 Light travels in straight lines Your experiment shows that light travels in straight lines. What every day consequences do you think this fact has? You can not see around corners. Shadows are formed in the area behind an object where light can not reach.
© Boardworks Ltd 2003 Seeing objects How do we see an object? Do we see all objects in the same way? There are two ways we see objects….. We see some objects because they are light sources. We see some objects by reflected light.
© Boardworks Ltd 2003 Seeing objects Light sourcesObjects seen by reflected light Sun Jupiter Firefly Moon Book Light bulb
© Boardworks Ltd 2003 Light sources How do light rays from the Sun and other light sources reach our eye? They travel in a straight line directly into our eye.
© Boardworks Ltd 2003 Reflected light How do light rays from a book and other such objects reach our eye? Light from the Sun or another light source strikes the book and some of the light is reflected into our eye.
© Boardworks Ltd 2003 Opaque and transparent materials Use a textbook or other source to find out what the words opaque and transparent mean. Opaque materials do not let light though. Transparent materials do let light through.
© Boardworks Ltd 2003 Opaque and transparent materials Hold different materials between a lamp and a screen. Material More or less opaque? Coal Water Glass Thin ice Coffee Fill in the results table shown estimating if the materials are more or less opaque than vegetable oil. more less more
© Boardworks Ltd 2003 Reflections There are two types of m____. F__ mirrors and c____ mirrors. Flat mirrors are known as p___ mirrors. If a mirror curves in then it is a c_____ mirror, if it curves out it is a c____ mirror. irrorslat urved lane oncave onvex
© Boardworks Ltd 2003 Plane mirrors Write out the letters of the alphabet down one side of a piece of paper, then next to the letter draw what the letter would look like as seen in a mirror. What do you predict the letter ‘L’ would look like in a mirror? What do you predict the letter ‘P’ would look like in a mirror?
© Boardworks Ltd 2003 Right and left What happens to writing in a mirror? The writing in a mirror is laterally inverted or back to front. If you are wearing a T-shirt with some writing on and wave your right hand what will your image appear like in a mirror? The writing on your T-shirt will be back to front and your image will be waving it’s left hand.
© Boardworks Ltd 2003 Rear-view mirrors Imagine you are driving along in your car…… …and then you look up and see the following in your mirror….. …with your knowledge of mirrors how must the writing be written on the vehicle?
© Boardworks Ltd 2003 Reading in Mirrors In small groups, take it in turns to read the list of words on the next slide with your back to the screen using a mirror. You can only move on to the next word when you read the first word correctly. Put your results in a table like this:
© Boardworks Ltd 2003 Words DogManBall BatBikeAnts ParkFinsPink LitterSandyShark
© Boardworks Ltd 2003 Results A)Who read the words in the quickest time? B)Plot a bar chart of you r results like: C)What was the average time taken in your group?
© Boardworks Ltd 2003 Image distance 1. Fix a plane mirror along the centre of a piece of A4 paper and draw around it. Place a pin as the object in front of the mirror. 2. Line up a ruler with the image of the pin and draw along the edge of the ruler on the paper. Repeat for 3 more positions of the ruler. 3. Remove the mirror and ruler. Where the lines cross is the image position. What are the distances between the mirror and object and its image? I
© Boardworks Ltd 2003 Image size and distance For a plane mirror how does the size of the image and the image distance from the mirror relate to the original object? Object Image Image size and object size are the same. The image distance is the same as the object distance from the mirror.
© Boardworks Ltd 2003 Investigating reflection Apparatus: Power pack Ray box Slit Plane mirror Protractor Ruler The ray box will get very hot, be careful when handling it.
© Boardworks Ltd 2003 Investigating reflection 1. Place the plane mirror on a piece of paper. 2. Draw a line across the front of the mirror. 3. Draw a normal to the mirror. 4. Shine rays of light at varying angles to the normal and record the position of the incident and reflected rays 5. Measure the incident angles and the reflected angles for each ray. Record your results in a table. Incident angle i Reflected angle r Reflected ray Incident ray
© Boardworks Ltd 2003 Results i rr 0°0° 30° 45° 70° 85° 0°0° 30° 45° 70° 85° What do you notice? Is there a pattern? Angle of incidence = Angle of reflection
© Boardworks Ltd 2003 Using plane mirrors By positioning two plane mirrors at 45° to each other at either end of a tube we can make a _________. periscope Periscopes are used in __________. submarines
© Boardworks Ltd 2003 Reflection : Curved Mirrors ƒ Chose a distant object [to get parallel rays of light]. Finding of a concave mirror. Hold the mirror in the other hand and move it closer to the screen until a clear image appears. Hold a plain white screen in one hand. Use a ruler to measure the distance between the lens and the screen - this is the focal length [ƒ].
© Boardworks Ltd 2003 Reflection : How does curvature affect ƒ? Concave mirrors reflect rays of light to a focal point. The distance between the mirror and the focal point is called the focal length [ƒ]. How can ƒ be changed? Concave mirrors produce real images because the rays of light meet [unless the object is close].
© Boardworks Ltd 2003 ƒ Take a piece of Al or stainless steel sheet and curve it slightly. Shine parallel rays of light at the reflector and plot their positions. Draw around the reflector. Measure ƒ and record your results. Carefully bend the reflector and repeat the process to see how ƒ changes with curvature. Reflection : How does curvature affect ƒ?
© Boardworks Ltd 2003 Reflection : Convex mirrors ƒ Convex mirrors reflect rays of light away from a focal point. The distance between the mirror and the focal point is called the focal length [ƒ] Convex mirrors produce virtual images - the rays of light do not meet.
© Boardworks Ltd 2003 Reflection : Curved mirrors Concave reflectors are used to focus signals from distant satellites. Convex reflectors are used to widen the field of view.
© Boardworks Ltd 2003 Which of the following is not a light source? A.The Sun B.A star C.Traffic lights D.A book
© Boardworks Ltd 2003 Which of the following is not seen by reflected light? A.Your hand B.Jupiter C.Light bulb D.The Moon
© Boardworks Ltd 2003 Which of the following is the most opaque? A.Milk B.Sea water C.Air D.Drinking water
© Boardworks Ltd 2003 What do we call the area behind an object where light can not reach? A.Transparent B.Shadow C.Opaque D.Outline
© Boardworks Ltd 2003 Which statement below is untrue for the image in a plane mirror? A.It is laterally inverted B.It is real C.It is same size as the object D.It is the same distance from the mirror as the object
© Boardworks Ltd 2003 Reflection 3.2 (a) Reflection of light Core Describe the formation, and give the characteristics, of an optical image by a plane.
© Boardworks Ltd 2003 Lenses. © Boardworks Ltd (c) Thin converging lens Core Describe the action of a thin converging lens on a beam of light.
© Boardworks Ltd of 20 © Boardworks Ltd of 47 KS3 Physics 8K Light.
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