Properties+of+waves+including+light+and+sound

= 3.2 Light =

Ray: The straight line in which light travels. A light ray is represented by a __ straight __ line with an __ arrow __ to show the direction of motion. Examples of source of light: Sun, Moon, Lamps, etc. How do we see an object and the colour of it?

3.2.1 Reflection of light

• Recall and use the law; angle of incidence = angle of reflection

__R eflection __: Light bounces off on the surface of an object. [|Image from utexas.edu]
 * Characteristics of an optical image by a plane mirror**

• Describe the formation of an optical image by a plane mirror, and give its characteristics • Recall that the image in a plane mirror is virtual Images from physicsclassroom.com || . .  .  .  .  || **Optical image by a plane mirror**
 * Ray diagram**: a diagram that traces the path that light takes in order for a person to view a point on the image of an object.
 * Supplement **
 * • Perform simple constructions, measurements and calculations based on reflections in plane mirrors **
 * [[image:Virtual image.gif width="365" height="258"]] || [[image:sciencelanguagegallery/Ray diagram.gif width="466" height="238"]]

1. A __ virtual __ image; Not a real image. It forms behind the mirror where light does not really come from (Indicate it as dotted lines). The image located behind the mirror is at the same distance from the object to the surface of the mirror.

2. An __ upright __ image.

3. L__ aterall __y i__ nverted __ image; Left-right reversal of the image.

4. The image has the same size as the object.

5. The image distance from mirror is the same as the object distance from mirror.

6. The image distance from the object is twice the distance from the mirror to the object. ||

Practice questions: 1. Light is reflected off the object and the rays strike into the mirror. The rays then are reflected back to our eyes. What is the size of the object in the mirror? Answer: It's the same as the size of the object. 2. What is the distance from the mirror of the image. Answer: It is the same as the distance between the mirror and the object. If the distance between the mirror and the object is 5cm, It's also 5cm. 3. To save expenses, you would like to buy the shortest mirror that will allow you to see your entire body. What is the minium lenght of the mirror you can buy? : The mirror needs to be only half your height. 4. A person 1.80 m tall stands in front of a plane mirror. What is the minimum height of the mirror, and how high must its lower edge be above the floor for the person to be able to see his/her whole body? Person’s eyes are 6.0 cm below the top of the head. [|Answer] from socratic.org

3.2.2 Refraction of light • Describe an experimental demonstration of the refraction of light • Use the terminology for the angle of incidence i and angle of refraction r and describe the passage of light through parallel-sided transparent material __R efraction __: Light changes its direction when it passes from one medium to another. The bending of light as it passes from one medium to another is called __r efraction .__ • Give the meaning of critical angle • Recall and use //n// = 1/sin c Critical angle: A special angle of __ incidence __ which it makes the angle of refraction at __ 90 __ degree.
 * || media type="youtube" key="7aU8sX8cFNs" width="560" height="315" || media type="youtube" key="MaGieycP9_U" width="560" height="315" ||
 * || [|GCSE Refraction] [|JamJarMMX] Published on 22 Apr 2012 || [|Water Waves - Shallow to Deep Water] [|GCSE Physics Ninja] Published on 18 Nov 2016 ||
 * [[image:refraction of wavefronts.gif width="264" height="275"]] || [[image:sciencelanguagegallery/a_level_physics_notes_snells_law_refraction_total_internal_reflection_critical_angle_html_m2fc87019.gif width="414" height="285"]] || [[image:Light-Refraction-Glass.gif width="346" height="258"]] ||
 * [|Image from http://electron6.phys.utk.edu] || [|Image from www.astarmathsandphysics.com] || [|Image from gcsescience.com] ||

• Describe internal and total internal reflection Total internal reflection: The complete reflection of a light ray at the boundary of two media, when the ray is in the medium with greater refractive index. Total internal reflection happens when the angle of incidence is greater than the critical angle of the medium.


 * Supplement **
 * • Recall and use the definition of refractive index //n// in terms of speed **

=

 * The measure of the bending of a ray of light when passing from one medium into another.** If //i// is the [|angle of incidence] of a ray in vacuum (angle between the incoming ray and the perpendicular to the surface of a medium, called the normal), and //r// is the [|angle of refraction] (angle between the ray in the medium and the normal), **the refractive index //n// is defined as the ratio of the sine of the angle of incidence to the sine of the angle of refraction**; //i.e., **n**// **= sin //i// / sin //r//**=====

**Refractive index is also equal to the velocity //c// of light** of a given frequency/wavelength **in empty space divided by its velocity //v// in a substance, or //n// = //c/////v//**.
[|The laws of refraction with examples] from www.physicstutorials.org
 * • Recall and use the equation sin //i// / sin //r// = //n// **

[|Lab report] (20%)
 * Snell’s law **

Total internal reflection occurs when light in a more dense medium reflects at the boundary. At a certain angle (when the angle of incidence is greater than the critical angle), light stays inside the cable/fiber. This characteristic of TIR allow us communicate faster and carries much more accurate information in optical fibre. This also allows us to do a key-hole surgery using an endoscope. Complete worksheet of total internal reflection and take notes on advantages of using optical fibres in your notebook.
 * • Describe the action of optical fibres particularly in medicine and communications technology **
 * media type="youtube" key="Sw7tA-fMnt4" width="560" height="315" || media type="youtube" key="KITxLGD3KPE" width="560" height="315" ||
 * [|Total Internal Reflection] [|LSGScience] Published on 28 Apr 2013 || [|Applications of total internal reflection] [|SPM Malaysia IPTV] Published on 11 Feb 2015 ||

3.2.3 Thin converging lens • Describe the action of a thin converging lens on a beam of light • Use the terms principal focus and focal length


 * Focal length:** The distance from the surface of a lens or mirror to its focal point.

**Principal focus:** The focal point. The point at which all radiation coming from a single direction and passing through a lens or striking a mirror converges. The point on the axis of a lens or mirror to which parallel rays of light converge or from which they appear to diverge after refraction or reflection


 * Principal ray:** The one ray within a bundle of incident rays that, upon entering an optical instrument from any given point of the object, passes through the optical centre of the lens.

• Draw ray diagrams to illustrate the formation of a real image by a single lens • Describe the nature of an image using the terms enlarged/same size/diminished and upright/inverted
 * media type="youtube" key="BrNB_BacIkA" width="560" height="315" || media type="youtube" key="fD1544bM_c4" width="560" height="315" || media type="youtube" key="8fUygzGO3b4" width="560" height="315" ||
 * [|Mr. Hamann's Ray Diagram Convex lens] [|leydenphysics] Published on 4 Apr 2011 || Bill Nye The Science Guy on [|Light Bending & Bouncing] [|Bill Nye] Published on 8 Apr 2009 || [|Mr. Hamann's Ray Diagram Concave lens] [|leydenphysics] Published on 4 Apr 2011 ||
 * Supplement **
 * • Draw ray diagrams to illustrate the formation of a virtual image by a single lens **
 * • Use and describe the use of a single lens as a magnifying glass **
 * • Show understanding of the terms real image and virtual image **

__Draw and interpret simple ray diagrams that illustrate the formation of real and virtual images by a single converging and a diverging lens.__ media type="custom" key="21856738" Operation of a thin lens applet by Andrew Adams, Nora Willett from Washington.edu ||  || Diverging lenses ray diagrams from physicsclassroom.com
 * Converging lenses ray diagrams from physicsclassroom.com

|| http://en.wikipedia.org/wiki/Lens_%28optics%29 ||  || Image formation by a diverging lens from http://www.colorado.edu/physics/phys1020/phys1020_sp05/labs/Lab4_Optics.htm || Ray diagrams for lenses and mirrors from physicsclassroom.com and [|hyperphysics]. [|Practice image] from courses.cs.washington.edu [|Image] from www.amherst.edu [|Refraction of light] from www.sciencelearn.org.nz
 * Image formation by a converging lens from
 * = **Image Check Points** ||= **Convex lens** ||= **Concave lens** ||
 * Position of the image ||  ||   ||
 * Real / Virtual ||  ||   ||
 * Inverted / Upright ||  ||   ||
 * Magnify / Diminish ||  ||   ||
 * Same / Opposite side ||  ||   ||

3.2.4 Dispersion of light Photograph by: Susan Schwartzenberg (c)1997, The [|Exploratorium] Core • Give a qualitative account of the dispersion of light as shown by the action on light of a glass prism including the seven colours of the spectrum in their correct order
 * Dispersion:** The phenomenon that a ray of light splits into its constituent colours (ROYGBIV) when light is passing through a transparent medium. The obtained band of colours due to the dispersion is called spectrum.

White light is made of various colours mixed together. The wavelength of visible light can vary from 400nm to 800nm. If it is passed through a prism, the each wavelength refracts by a different amount and therefore a different angle. It disperse/splits into a band of colour spectrum.

// Questions to think: // 1. Which colour will you see at the top of the seperated spectrum? 2. Can you make the spectrum of light back into white light? 2. Why does a prism split visible light into the spectrum of rainbow colours?

1. Draw the separation of the spectrum on the other side of the prism. Don't forget to indicate normal on each boundry. 2. Determine the refractive index of each red and blue monochromatic light using Snell's law with the angle of incidence and the angle of refraction you measured from task 1. [|Refraction Through a Prism] by tutorVista from youtube.com [|Index of refraction of glass] from hypertextbook Go to S-Cool websites for dispersion and TIR
 * // Task: //**
 * media type="youtube" key="uucYGK_Ymp0" width="560" height="315" || media type="youtube" key="Aggi0g67uXM" width="560" height="315" || media type="youtube" key="UCiu2IA4Lmg" width="560" height="315" ||
 * [|Newton's Prism Experiment] [|MITK12Videos] Published on 7 Mar 2013 || [|Refraction: why glass prisms bend and separate light] [|ABC Education] Published on 24 Feb 2014 || [|Refraction of light through a prism] [|Jumeirah College Science] Published on 27 Jan 2013 ||

**monochromatic**: containing or using only one color.  "monochromatic light" - light or radiation of a single wavelength or frequencyof light (Red laser is monochromatic) (e) Electromagnetic spectrum media type="youtube" key="IXxZRZxafEQ" width="560" height="315" What is light? [|Kurzgesagt – In a Nutshell] Published on 15 Oct 2015 Take notes using [|Electromagnetic spectrum] BBC Bitesize then complete the test on the last page  <span style="bottom: 0px; display: block; flex: 0 0 auto; height: 94px; left: 0px; margin-left: auto; margin-right: auto; overflow: hidden; position: absolute; right: 0px; text-decoration-line: none; top: 0px; width: 168px;"> <span style="display: inline-block; flex: 1 1 1e-09px; min-width: 0px; padding-right: 24px; text-decoration-line: none;">[|===Newton's Prism Experiment=== MITK12Videos690K views]
 * Supplement **
 * • Recall that light of a single frequency is described as monochromatic **

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