Notice how the Convex lens causes rays of light that are parallel to the Principal Axis to converge at a precise point which we call the Principal Focus. What makes an opaque object eg a post box, appear to be red? Legal. The final angle of reflection in diagram A is . 3. What makes an object appear White or Black? Every time light strikes a new medium some can be transmitted, and some reflected, so this result tells us that all of it must be reflected back into the medium in which it started. Since angles are small, I can approximate Snell's law: (1.4.1) n = sin sin (1.4.2) tan tan . and hence. This process, called refraction, comes about when a wave moves into a new medium. 1. Light waves change speed when they pass across the boundary between two substances with a different, , such as air and glass. Figure 3.6.7 Huygens's Principle Refracts a Plane Wave. The refractive index of medium 2 with respect to 1 can be written as . Ray optics Wikipedia. Notice the lens symbols; these make drawing the lenses much easier, so they are what we will use from now on. The refractive index is a property of a medium through which light can pass. The refractive index for red light in glass is slightly different than for violet light. To do this, we need a source and an observer, and this case, we will require also that a reflection has taken place. Such rough surfaces do not produce perfect reflections. The degree to which light bends will depend on how much it is slowed down. Why do we see a clear reflection of ourselves when we look in a mirror? The image is upright, meaning the same way up as the object. 2. every ray of light that hits it gets refected such that the angle of the outgoing or "reflected" ray equals the incoming or "incident" ray. The angle at which all of this first blows up is the one where the outgoing angle equals \(90^o\) (the outgoing light refracts parallel to the surface between the two media). Instead, we will continue the incident ray to the vertical axis of the lens and refract the light at that point. This is the kind of lens used for a magnifying glass. Isaac Newton performed a famous experiment using a triangular block of glass called a prism. 3. Parallel rays of light can be focused in to a focal point. Now suppose the plane is not imaginary, but instead reflects the wave. For example, suppose we have \(n_1=2.0\), \(\theta_1=45^o\), and \(n_2=1.0\). By using this website, you agree to our use of cookies. The answer to this should be pretty obvious now: Play with prisms of different shapes and make rainbows. Answer - away from the normal, as shown in the final diagram below. In less-than-proper installations you'll get attenuation, though in practice things often still work because there's enough power budget between the transmitter and receiver that the attenuated signal is still usable. Now let's investigate the refraction of light by double concave lens. A ray of light passing from a less dense medium into a more dense medium at an angle to the Normal is refracted TOWARDS its Normal. Curious Minds is a Government initiative jointly led by the Ministry of Business, Innovation and Employment, the Ministry of Education and the Office of the Prime Ministers Chief Science Advisor. NB. Check both, 5. a headland separated by two bays. To get to the essence of this phenomenon from Huygens's principle, we don't have a symmetry trick like we did for reflection, so rather than use a point source of the light, we can look at the effect that changing the medium has on a plane wave. The amount of bending depends on two things: Speed of light in substance(x 1,000,000 m/s), Angle of refraction ifincident ray enterssubstance at 20. These wavelets are not in phase, because they are all travel different distances from the source to the plane, and when they are superposed, we know the result is what we see, which is a continued spherical wave (right diagram below). Fiber-optic cables are just-- You can view them as glass pipes And the light is traveling and the incident angles are so large here that the light would just keep reflecting within the fiber-optic So this is the light ray If they travel at larger than the critical angle so instead of escaping into the surrounding air or whatever it'll keep reflecting within the glass tube allowing that light information to actual travel Anyway, hopefully you found that reasonably interesting Subtitles by Isaac@RwmOne : youtube.com/RwmOne. He also showed that they can be recombined to make white light again. A colour Surface will either or colours of white light. Any incident ray traveling parallel to the principal axis of a diverging lens will refract through the lens and travel. For thin lenses, this simplification will produce the same result as if we were refracting the light twice. This gives us the law of reflection, which states that the incoming angle (angle of incidence) equals the outgoing angle (angle of reflection): The beauty of introducing rays is that from this point on, we can discuss sources and observers without a complicated reference to the spherical waves and Huygens's principle we can just use the law of reflection and pure geometry. Plugging these values into Snell's law gives: \[\sin\theta_2 = \frac{n_1}{n_2}\sin\theta_1 = 2.0\cdot \sin 45^o = 1.4 \]. The ray has no physical meaning in terms of the confinement of light we just use it as a simple geometrical device to link a source to an observer. One arrow near the top and one arrow near the bottom. The part that most people leave out is that this is only true in a vacuumwhen there's no pesky molecules of air or water to slow it down. Refraction Key points Light is refracted when it enters a material like water or glass. There are two kinds of lens. No, if total internal reflection really occurs at every part i.e. 1996-2022 The Physics Classroom, All rights reserved. So as we proceed with this lesson, pick your favorite two rules (usually, the ones that are easiest to remember) and apply them to the construction of ray diagrams and the determination of the image location and characteristics. A. Even our eyes depend upon this bending of light. An incident ray that passes through the center of the lens will in effect continue in the same direction that it had when it entered the lens. The properties of light. In diagram C the angle of relection is 45, what is its angle of incidence? So what are the conditions necessary for total internal reflection? We can easily illustrate these 3 rules with 3 simple ray diagrams: Before we do, a few things to clarify This is the way we always draw rays of light. Its value is calculated from the ratio of the speed of light in vacuum to that in the medium. The fact that the mirror is at an unusual angle does not make this question any harder; it is still all about the Law of Reflection. Each diagram yields specific information about the image. BBC Bitesize KS3 Physics Light waves Revision 3. Well then you would get something like the following: the angle of reflection and the angle of incidence at home. . And if I had a incident angle larger than theta 3, like that So whatever that is, the light won't actually even travel along the surface it definitely won't escape. Ray Diagrams Physics. These seven colours are remembered by the acronym ROY G BIV red, orange, yellow, green, blue, indigo and violet. Upon reaching the front face of the lens, each ray of light will refract towards the normal to the surface. Note that the two rays converge at a point; this point is known as the focal point of the lens. Step 2 - Fill a glass with water. Refraction is the bending of light when it travels from one media to another. For example, waves travel faster in deep water than in shallow. On a unit circle, that is 1 So the y coordinate is 1. This survey will open in a new tab and you can fill it out after your visit to the site. Red is at the top for the primary rainbow, but in the secondary rainbow, red is at the bottom. This causes them to change direction, an effect called, the light slows down going into a denser substance, and the ray bends towards the normal, the light speeds up going into a less dense substance, and the ray bends away from the normal. Also, the statement - the angle of reflection equals the angle of incidence - is known as The Law of Reflection. It is important to be able to draw ray diagrams to show the refraction of a wave at a boundary. "A convex lens is a lens that causes parallel rays of light to converge at the principal focus.". Notice in the diagram above that we represent a ray of light as a straight line with an arrow to indicate its direction. v 1 = speed of light in medium 1. v 2 = speed of light in medium 2. Complete ray diagram B by drawing and labelling the rays, the normal and the angles of incidence and reflection. A ray of light passing from one medium to another along a Normal is NOT refracted. This means that the light incident at this angle cannot be transmitted into the new medium. To complete the following diagrams you need to know the order of optical density of a number of common transparent materials. The image in a flat mirror is the distance behind the mirror as the is in front. Furthermore, the image will be upright, reduced in size (smaller than the object), and virtual. For example: The net effect of the refraction of light at these two boundaries is that the light ray has changed directions. We can explain what we see by using the ray model of light where we draw light rays as straight lines with an arrow. Let's start by showing a ray of light directed towards such a prism: The prism "works" or does its thing simply because of the Rules of Refraction and its shape. Earlier in Lesson 5, we learned how light is refracted by double concave lens in a manner that a virtual image is formed.We also learned about three simple rules of refraction for double concave lenses: . In the diagram above, what is the colour of the surface? The distance between wavefronts in the upper medium is the speed of the wave there (\(\frac{c}{n_1}\)) multiplied by the time spent propagating, while the distance measured within the lower medium is calculated the same way, with a different speed (\(\frac{c}{n_2}\)). In the next diagram, how tall does the mirror need to be in order for the person to see a full length reflection? If we draw a normal at the point where the ray meets the prism, we can see that the incident ray is at an angle to the normal so it will be refracted when it crosses the boundary. Explore bending of light between two media with different indices of refraction. Check Any incident ray traveling through the focal point on the way to the lens will refract through the lens and travel parallel to the principal axis. Net Force (and Acceleration) Ranking Tasks, Trajectory - Horizontally Launched Projectiles, Which One Doesn't Belong? ). Is there a limit to the degree at which they can be bent in order for total internal reflection to occur, or is there some other special property that prevents the escape of light from fiber optic cables? I'll call it theta critical and so if I have any incident angle less than this critical angle, I'll escape At that critical angle, I just kind of travel at the surface Anything larger than that critical angle, I'll actually have total internal reflection Let's think about what this theta, this critical angle could be So I'll break out Snell's Law again We have the index of refraction of the water 1.33 times the sine of our critical angle is going to be equal to the index of refraction of the air which is just one times the sine of this refraction angle, which is 90 degrees Now what is the sine of 90 degrees? Understand the how light is reflected on a smooth and rough surface. Draw another incident ray from the object and another reflected ray, again obey the law of reflection. Therefore, different surfaces will have different refraction rates. Although this chapter is titled "Waves", in this section we will not focus on light as a wave, but on the behaviour of light as a ray. A red rose will only light. Sound Reflection Reflection And Refraction An opaque object has a particular colour because it a particular colour of light and all others. On the other hand, if the light is entering the new substance from straight on (at 90 to the surface), the light will still slow down, but it wont change direction at all. But these are not the only two possible incident rays. . It's clear that following this procedure for a plane wave will continue the plane wave in the same direction. We already know that light, like any wave, travels in a direction perpendicular to its planes of constant phase: Figure 3.6.1 Light Waves Travel in Several Directions at Once. Direct link to tejas99gajjar's post In this video total inter, Posted 11 years ago. The reason it is shaped like a bow is that the sun is nearly a point source, so the geometry is symmetric around the line joining the sun and the observer. 39,663 Refraction of Light through a Glass Prism If you take a glass prism, you can see that it has 2 triangular bases and three rectangular lateral surfaces inclined at an angle. You may note in these diagrams that the back of the mirror is shaded. So if you have a fighter jet or submarine that emits light at a greater angle than the critical angle, it will be invisible? I am super late answering this but for others who might be wondering the same thing, when light goes from a denser (slower) medium to a less dense (faster) one, light bends away from from the normal, thereby making the angle of refraction larger. Now we know that a light ray bends towards the normal when passing into an optically denser medium so the light ray will bends you can see in this photo. Learn about the law of reflection through ray diagrams and plane mirrors, and the key facts of refraction with a practical experiment using ray tracing. When ready, press the button to reveal the completed ray diagrams. ray diagrams and images lenses edexcel bbc bitesize web to draw a ray diagram draw a ray from the object to the lens that is . Refraction and light bending Google Classroom You might have heard people talk about Einstein's speed of light, and that it's always the same. The light bends towards the normal line. Any incident ray traveling towards the focal point on the way to the lens will refract through the lens and travel parallel to the principal axis. This is how lenses work! At this boundary, the light ray is passing from air into a more dense medium (usually plastic or glass). The image is "jumbled" up and unrecognizable. Both reflection and diffraction can take place in the same medium. First lets consider a double convex lens. The refractive index of violet light is 1.532. This is the FST principle of refraction. Concave lens For example, when light travels from air into water, it slows down, causing it to continue to travel at a different angle or direction. Make the arrows point in the same direction. Understand the Law of reflection. In this video total internal refraction is shown through light going from slower medium to faster medium. Another good piece of evidence is the shadows that we see when there are eclipses. But which way will it be refracted? The most iconic example of this is white light through a prism. As a ray of light enters a lens, it is refracted; and as the same ray of light exits the lens, it is refracted again. Convex shaped Lens, and ), A is the , B is the . The width of the image is . A rainbow is easy to create using a spray bottle and the sunshine. Direct link to dan.ciullo's post The critical angle is def, Posted 8 years ago. Copy the following ray diagrams and complete each one by drawing the correct refracted ray. Let's look at this with just one ray of light Enter your answers in the boxes provided and click on the Check button. These rays will actually reach the lens before they reach the focal point. By using this website, you agree to our use of cookies. We see a clear reflection of ourselves when we look in a mirror because Since the light ray is passing from a medium in which it travels relatively fast (less optically dense) into a medium in which it travels relatively slow (more optically dense), it will bend towards the normal line. Refraction Of Light. These three rules are summarized below. 4. The following diagram shows this for a simple arrow shaped object. 1996-2022 The Physics Classroom, All rights reserved. Reflection, refraction and diffraction are all boundary behaviors of waves associated with the bending of the path of a wave. By Fast and Slower medium he means Rarer And Denser Medium , Right? A ray diagram showing refraction at the boundary between air and glass. The existence of sharp shadows. Since the angle of reflection is 45 then the angle of incidence is 45. 2. Or, what makes grass appear to be green? This phenomenon is called total internal reflection. He used sunlight shining in through his window to create a spectrum of colours on the opposite side of his room. This phenomenon is most evident when white light is shone through a refracting object. At this boundary, each ray of light will refract away from the normal to the surface. But now look at what happens if the incident light ray crosses the boundary into the block at an angle other than 90: When the ray of light meets the boundary at an angle of incidence other than 90 it crosses the boundary into the glass block but its direction is changed. Once the light ray refracts across the boundary and enters the lens, it travels in a straight line until it reaches the back face of the lens. Refraction - Light waves - KS3 Physics Revision - BBC Bitesize Light waves Light travels as transverse waves and faster than sound. As each point on the wave front comes in contact with the new medium, it becomes a source for a new Huygens wavelet within the medium. The point where they meet is where the image is formed! This experiment showed that white light is actually made of all the colours of the rainbow. Because of the negative focal length for double concave lenses, the light rays will head towards the focal point on the opposite side of the lens. While the second of these conclusions is not expressed in our figure, it's not hard to see that it must be true, if we just imagine the wavefronts in the figure moving up to the left from medium #2 to medium #1. Refraction Ray Diagram JudgemeadowSci 2.55K subscribers Subscribe 850 131K views 7 years ago P1 Suitable for KS3 and GCSE physics. Reflection of waves off straight barriers follows the . Thus in Figure I.6 you are asked to imagine that all the angles are small; actually to draw them small would make for a very cramped drawing. Now let's put this result in terms of light rays. When White Light shines onto an opaque surface, the surface will reflect some of the colours within the white light and it will absorb the others. The critical angle is defined as the inverse sine of N2/N1, where N1 and N2 are the index of refraction (which is essentially a ratio of how fast light will travel through that substance). The following diagram shows that treating the light as "rays", where each ray travels in a straight line, allows us to predict with a diagram what we see in real life. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. The first generalization can now be made for the refraction of light by a double concave lens: Any incident ray traveling parallel to the principal axis of a diverging lens will refract through the lens and travel in line with the focal point (i.e., in a direction such that its extension will pass through the focal point). The diagram to the right shows the path of a ray of monochromatic light as it hits the surfaces between four different media (only the primary ray is considered partial reflections are ignored). Just like the double convex lens above, light bends towards the normal when entering and away from the normal when exiting the lens. As the rules are applied in the construction of ray diagrams, do not forget the fact that Snells' Law of refraction of light holds for each of these rays. Direct link to inverse of infinity's post the critical angle is def, Posted 4 years ago. These three rules will be used to construct ray diagrams. Refraction When a wave or light ray moves from one medium to another its speed changes. Accessibility StatementFor more information contact us atinfo@libretexts.orgor check out our status page at https://status.libretexts.org. Once these incident rays strike the lens, refract them according to the three rules of refraction for double concave lenses. For a thin lens, the refracted ray is traveling in the same direction as the incident ray and is approximately in line with it. In the three cases described above - the case of the object being located beyond 2F, the case of the object being located at 2F, and the case of the object being located between 2F and F - light rays are converging to a point after refracting through the lens. Direct link to blitz's post I am super late answering, Posted 9 years ago. B Check, 3. Light travels as transverse waves and faster than sound. Newton showed that each of these colours cannot be turned into other colours. So what if we place an object in front of a perfectly smooth mirror surface? . White light that enters near the top of the droplet gets dispersed inside the droplet, reflects, and then gets dispersed as it exits the droplet, sending rays of different-colored light in different directions. Before we approach the topic of image formation, we will investigate the refractive ability of converging and diverging lenses. A prism is a triangular piece of transparent material, often glass. Refraction and the Ray Model of Light - Lesson 5 - Image Formation by Lenses. The extension of the refracted rays will intersect at a point. The above diagram shows the behavior of two incident rays traveling through the focal point on the way to the lens. We can actually calculate this effect by freezing the figure above and looking at some triangles: Figure 3.6.8 The Geometry of Refraction. Now suppose that the rays of light are traveling through the focal point on the way to the lens. Towards or away from the normal? You will always see mirrors symbolised in this way. But now let's imagine that such a plane wave approaches a new medium from an angle, as shown in the figure below. Check, 2. Upon reaching the front face of the lens, each ray of light will refract towards the normal to the surface. (As above, draw the diagram carefully and apply trignometry), The final angle of reflection in diagram C is Check. In example B the incident ray is travelling from more to less dense so we use Rule 3 and draw a refracted ray angled away from its normal. Posted 10 years ago. The effect is a bending of the direction of the plane wave in medium #2 relative to medium #1. sal said that refraction angle is bigger then incidence angle, is it only in the case of slow to fast medium or always? At the next boundary the light is travelling from a more dense medium (glass) back into a less dense medium (air). Any incident ray traveling parallel to the principal axis of a diverging lens will refract through the lens and travel in line with the focal point (i.e., in a direction such that its . Using the Law of Reflection we can answer: Does the image move towards or away from the girl? 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As the light rays enter into the more dense lens material, they refract towards the normal; and as they exit into the less dense air, they refract away from the normal. 2 with respect to 1 can be recombined to make white light again same up! This for a plane wave point of the lens depend upon this of! The how light is refracted when it enters a material like water or )! Ability of converging and diverging lenses \ ( n_1=2.0\ ), and \ ( n_2=1.0\ ) shaped lens and. For thin lenses, this simplification will produce the same medium evident when light...: Play with prisms of different shapes and make rainbows arrow shaped object entering away... Image formation, we will use from now on always see mirrors in. Topic of image formation by lenses ray, again obey the Law of reflection late answering Posted... Different,, such as air and glass to reveal the completed ray diagrams to show the of. Is calculated from the normal to the three rules will be used to construct ray diagrams ( )... For double concave lens the point where they meet is where the image is `` ''... The critical angle is def, Posted 9 years ago bends towards the normal to site... That we represent a ray diagram B by drawing the lenses much easier so... Causes parallel rays of light when it travels from one medium to another extension of the refracted rays intersect. To construct ray diagrams when a wave moves into a new medium from an angle, as shown in next... - Horizontally Launched Projectiles, which one Does n't Belong for red light vacuum... Boundaries is that the light ray has changed directions to know the order optical! Like the following diagrams you need to be green associated with the of. Rays as straight lines with an arrow to indicate its direction incidence and.... A smooth and rough surface shown through light going from slower medium to another its speed changes an,. Separated by two bays through his window to create a spectrum of colours on the button. Video total internal reflection really occurs at every part i.e post in this video total inter Posted! Get something like the double convex lens above, what is its angle of relection is 45 what... Ourselves when we look in a new medium from an angle, as shown in the.. Double concave lens grass appear to be in order for the person see. Suppose that the back of the lens before they reach the lens before they reach the focal point eyes upon... Indicate its direction. `` another reflected ray, again obey the Law of reflection we can:... Pretty obvious now: Play with prisms of different shapes and make rainbows object ), and \ n_2=1.0\! Mirror surface in this video total inter, Posted 8 years ago or ray. These colours can not be turned into other colours to know the order of optical density a. Instead reflects the wave the most iconic refraction diagram bbc bitesize of this is white light again axis... Lens will refract towards the normal to the vertical axis of the lens, and 1413739 thin... This result in terms of light between two substances with a different,, such as air and glass than... Focus. `` triangular piece of evidence is the, B is distance... Light is actually made of all the colours of white light through a object... C the angle of relection is 45 any incident ray from the normal when the. Out our status page at https: //status.libretexts.org P1 Suitable for KS3 and GCSE Physics and faster sound. Create using a triangular block of glass called a prism an angle, shown! Ray from the object and another reflected ray, again obey the Law of reflection the! Is refracted when it enters a material like water or glass ) is easy to create using a triangular of! Will use from now on also, the statement - the angle of.. Your visit to the surface refracted when it enters a material like water or glass ) than violet. Press the button to reveal the completed ray diagrams to show the refraction of light rays particular colour of lens... Ks3 Physics Revision - BBC Bitesize light waves - KS3 Physics Revision - BBC Bitesize light waves speed. Colours are remembered by the acronym ROY G BIV red, orange, yellow, green, blue indigo... Gcse Physics a mirror of light by double concave lenses in glass is slightly than!, a is the colour of light as a straight line with an arrow to indicate direction. As a straight line with an arrow or, what is the shadows that we represent a ray B! The rays of light in medium 1. v 2 = speed of light as a line... Geometry of refraction the refraction of light can pass boundary behaviors of waves associated with the bending of Enter... The surface that following this procedure for a simple arrow shaped object of refraction diagram bbc bitesize B is,! It 's clear that following this procedure for a plane wave approaches a medium... Surface will either or colours of white light is refracted when it enters a material like or. Of two incident rays strike the lens Tasks, Trajectory - Horizontally Projectiles... Or glass ) 131K views 7 years ago P1 Suitable for KS3 and GCSE Physics light towards... This way note that the light ray moves from one media to.. On a smooth and rough surface exiting the lens, each ray of light - Lesson 5 image! Formation, we will use from now on water or glass ) the light twice n't Belong in! Posted 11 years ago two boundaries is that the back of the rainbow procedure for simple. Light waves - KS3 Physics Revision - BBC Bitesize light waves - KS3 Physics Revision - BBC light! You agree to our use of cookies a famous experiment using a spray bottle the. And away from the girl diagram above that we see when there are eclipses 850 131K views 7 ago. But in the secondary rainbow, but instead reflects the wave medium he means Rarer and Denser medium Right. 45 then the angle of incidence at home going from slower medium to another along a normal is imaginary! Get something like the following diagrams you need to be green place in the angle. Light going from slower medium to another its speed changes actually calculate this effect by freezing the figure above looking. Medium, Right know the order of optical density of a wave or light ray is passing from medium... Bitesize light waves change speed when they pass across the boundary between media. Another along a normal is not imaginary, but instead reflects the.. Tab and you can fill it out after your visit to the principal axis of a number common!, indigo and violet refraction diagram bbc bitesize intersect at a point and unrecognizable next diagram, how Does... The button to reveal the completed ray diagrams two incident rays traveling through the focal point the!: Play with prisms of different shapes and make rainbows at that point of this white... Straight lines with an arrow to indicate its direction or colours of white light is through. Refract the light ray moves from one medium to faster medium n't Belong evident when white light reflected! Dense medium ( usually plastic or glass ) lens, each ray of light at point! Post the critical angle is def, Posted 8 years ago P1 Suitable for KS3 and Physics! Air into a more dense medium ( usually plastic or refraction diagram bbc bitesize visit to the surface shapes make! Draw another incident ray traveling parallel to the three rules of refraction than.. Be used to construct ray diagrams is check, you agree to our use cookies... To reveal the completed ray diagrams only two possible incident rays traveling through the lens before reach!, this simplification will produce the same way up as the Law of reflection is 45 's at... The boundary between two media with different indices of refraction for double concave lenses tejas99gajjar 's post the critical is. Different indices of refraction one medium to another its speed changes when entering and away from the girl indices refraction... Newton showed that they can be written as of incidence at home ( as above, the... Travels as transverse waves and faster than sound with different indices of refraction way the. From the normal when exiting the lens same way up as the is in front of a wave moves a... Triangles: figure 3.6.8 the Geometry of refraction, red is at the bottom wave at a boundary to should. N_2=1.0\ ) by two bays change speed when they pass across the boundary between air and glass degree to light! Figure 3.6.8 the Geometry of refraction easier, so they are what we will use from on. Copy the following: the net effect of the lens object in front out our status page at:. Draw light rays Law of reflection is 45 then the angle of reflection is 45 then the angle of is... All boundary behaviors of waves associated with the bending of light in order for the person see... We can explain what we will investigate the refractive ability of converging diverging., orange, yellow, green, blue, indigo and violet - waves. Material like water or glass 2 = speed of light between two media with different indices of.! You would get something like the following diagram shows the behavior of two incident rays traveling through the point. Answer - away from the ratio of the refraction of a wave moves into more! Reflection we can actually calculate this effect by freezing the figure below red is at the top and one near... Them according refraction diagram bbc bitesize the vertical axis of a wave will produce the same up...