KS4 Physics Lesson slide on Behaviour of Light.pptx

Presentation on Light

1. The Behaviour of Light Class: KS4 Subject: Physics

2. Learning Objectives Understand the principles of reflection, refraction, diffraction and interference Grasp the concept of polarization and doppler effect. Apply these principles in practical situations and experiments 01. 02. 03.

3. Sub-topics to Consider 01. 04. 02. 05. 03. 06. Principle of Diffraction Interference of Light waves Polarization and Doppler Effect Introduction to Light Principle of Reflection Principle of Refraction

4. Introduction to Light 01. What is Light? Properties of Light Electromagnetic Spectrum

5. Introduction to Light waves What is Light? Light is a type of electromagnetic wave. Electromagnetic waves Electromagnetic waves are waves that can travel through the vacuum of outer space. Unlike sound waves, which need a medium (like air or water) to travel through, electromagnetic waves do not require a medium . They are created by the movement of electric charges and are composed of oscillating electric and magnetic fields.

6. Introduction to Light waves continued Properties of Light Speed: Light travels approximately 300,000 kilometres per second (km/s) in a vacuum . Wavelength: The distance between consecutive peaks of the wave. Visible light has wavelengths between 400 nm (nanometers) and 700 nm . Frequency: The number of wave peaks that pass a point in one second. It's measured in Hertz (Hz).

7. Intro to Light waves cont’d Visible Light This is the light we can see with our eyes. It includes all the colors of the rainbow . Each color corresponds to a different wavelength, with red having the longest wavelength and violet having the shortest. The Electromagnetic spectrum The electromagnetic spectrum includes all types of electromagnetic waves, ranging from very long wavelength radio waves to very short wavelength gamma rays. Visible light is a small part of this spectrum, which includes red (longest wavelength) to violet (shortest wavelength).

8. Electromagnetic Spectrum

9. Electromagnetic spectrum Type of radiation Wavelength (pm) Frequency (hertz) Energy (joules) Radio waves > 1 x 10^5 pm < 3 x 10^9 Hz < 2 x 10^-24 J Microwaves 1 mm - 1 m 3 x 10^9 Hz - 3 x 10^11 Hz 2 x 10^-24 J - 2 x 10^-22 J Infrared 700 nm - 1 mm 3 x 10^11 Hz - 4.3 x 10^14 Hz 2 x 10^-22 J - 2.9 x 10^-19 J Visible light 400 nm - 700 nm 4.3 x 10^14 Hz - 7.5 x 10^14 Hz 2.9 x 10^-19 J - 5 x 10^-19 J Ultraviolet 10 nm - 400 nm 7.5 x 10^14 Hz - 3 x 10^16 Hz 5 x 10^-19 J - 2 x 10^-17 J X-rays 0.01 nm - 10 nm 3 x 10^16 Hz - 3 x 10^19 Hz 2 x 10^-17 J - 2 x 10^-14 J Gamma rays < 0.01 nm > 3 x 10^19 Hz > 2 x 10^-14 J

10. Principle of Reflection 02. Definition Law of Reflection Illustration and Implementations

11. Law of Reflection   The Law of Reflection states that when a light ray hits a smooth surface, the angle of incidence (the angle between the incoming ray and the normal to the surface) is equal to the angle of reflection (the angle between the reflected ray and the normal). Definition Mathematical representation

12. Illustration of Law of Reflection The incident ray, the reflected ray, and the normal (a line perpendicular to the surface at the point of incidence) all lie in the same plane.

13. Implementation of The Law of Reflection Plane Mirror Periscope

14. Principle of Refraction 03. What is Refraction? Snell’s Law

15. Law of Refraction Here, and are the refractive indices of the two media, and and are the angles of incidence and refraction, respectively. The refractive index is a measure of how much the speed of light is reduced inside the medium . NOTE: The incident angle is the angle between the incident ray and the normal to the surface while the refracted angle is the angle between the refracted ray and the normal   The Law of Refraction, also known as Snell's Law, states that when a light ray passes from one medium into another, it bends or refracts. Snell’s Law Mathematical representation What is Refraction? This is the bending of a light ray as it crosses the boundary between two media of different densities, thus causing a change in its direction.

16. Illustration of The Law of Refraction

17. Implementation of The Law of Refraction Lens Prism

18. Principle of Diffraction 04. What is Diffraction? Conditions for Diffraction

19. What is Diffraction? Diffraction Pattern: When light passes through a single slit, it creates a central bright fringe (or band) with several dimmer fringes on either side. The pattern results from the interference of the light waves spreading out after passing through the slit . Double-Slit Experiment: In a double-slit experiment, light passing through two close slits creates an interference pattern of alternating bright and dark fringes on a screen. This is due to constructive and destructive interference of the light waves emanating from the two slits. Wave Behavior: Diffraction demonstrates the wave nature of light. When light encounters an obstacle or a slit that is comparable in size to its wavelength, it bends around the edges and creates patterns of light and dark regions. Definition Diffraction is the bending and spreading out of light waves as they pass around an obstacle or through a narrow slit

20. Condition for Diffraction As a general rule: If wavelength > obstacle/aperture size: Strong diffraction If wavelength ≈ obstacle/aperture size: Moderate diffraction If wavelength < obstacle/aperture size: Minimal diffraction For a slit or aperture, the condition for observing a clear diffraction pattern is often given by : Where: a = width of the slit or aperture λ = wavelength of the wave   Significant diffraction occurs when the wavelength is comparable to or larger than the size of the obstacle or aperture . For obstacles, a similar condition applies. Diffraction effects become noticeable when the size of the obstacle is comparable to or smaller than the wavelength. The conditions for diffraction depend on the relationship between the wavelength of the wave and the size of the obstacle or aperture it encounters. Here are the key points:

21. Illustration of Diffraction The angle of diffraction (θ) is related to the wavelength and aperture size by the equation: This shows that longer wavelengths and smaller apertures lead to larger diffraction angles.  

22. More things to note on diffraction… All electromagnetic waves can bend (diffract) to some degree, regardless of their wavelength. The key is the relationship between the wavelength and the size of the obstacle or aperture. Waves with longer wavelengths (like radio waves) diffract more noticeably around everyday objects . While Waves with shorter wavelengths (like visible light, X-rays, gamma rays) require much smaller obstacles or apertures to show noticeable diffraction effects. For example: Radio waves (long wavelength) diffract noticeably around buildings. Visible light (shorter wavelength) diffracts noticeably around the edge of a razor blade or through a narrow slit. X-rays (very short wavelength) diffract noticeably when passing through a crystal lattice. .01 .02 .03

23. Principle of Interference 05. What is Interference? Types of Interference Coherent Sources Young’s Double-slit Experiment Conditions for Light Interference

24. What is Interference? Definition  Interference is the phenomenon in which two waves superpose to form the resultant wave of the lower, higher or same amplitude.  The most commonly seen interference is the optical interference or light interference. This is because light waves are generated randomly by most of the sources. This means that light waves coming out of a source do not have a constant amplitude, frequency or phase. The most common example of interference of light is the soap bubble which reflects wide colours when illuminated by a light source.

25. Types of Interference In destructive interference, the crest of one wave falls on the trough of another wave such that the amplitude is minimum. The displacement and phase of these waves are not the same. Constructive interference Constructive interference takes place when the crest of one wave falls on the crest of another wave such that the amplitude is maximum. These waves will have the same displacement and are in the same phase. Destructive interference

26. Illustration of The Types of Interference

27. Coherent Sources Definition Two sources are said to be coherent when the waves emitted from them have the same frequency and constant phase difference. Examples of coherent sources are: Laser light is an example of a coherent source of light. The light emitted by the laser light has the same frequency and phase. Sound waves are another example of coherent sources. The electrical signals from the sound waves travel with the same frequency and have constant phase difference. Characteristics The waves generated have a constant phase difference The waves are of a single frequency Illustration of coherent sources

28. Young’s Double-Slit Experiment The great scientist Young performed an experiment to prove the wave nature of light by explaining the phenomenon of interference of light. In Young’s double slit experiment, two coherent sources were generated using diffracted light from a single slit. Note that the waves must have a constant phase difference, so the two slits need not be placed symmetrically from the first slit to observe an interference pattern. 

29. Conditions for Interference of Light Waves For sustained interference of light to occur, the following conditions must be met: Coherent sources of light are needed. Amplitudes and intensities must be nearly equal to produce sufficient contrast between maxima and minima. The source must be small enough that it can be considered as a point source of light. The interfering sources must be near enough to produce wide fringes. The source and screen must be far enough to produce wide fringes. The sources must emit light in the same state of polarization. The sources must be monochromatic.

30. Polarization and Doppler Effect 06. What is Polarization? Types of Polarization Methods used in Light Polarization Applications What is Doppler Effect?

31. What is polarization? Light is the interaction of electric and magnetic fields travelling through space. The electric and magnetic vibrations of a light wave occur perpendicularly to each other. The electric field moves in one direction and the magnetic field in another ‘perpendicular to each other. So, we have one plane occupied by an electric field, another plane of the magnetic field perpendicular to it, and the direction of travel is perpendicular to both. These electric and magnetic vibrations can occur in numerous planes. A light wave that is vibrating in more than one plane is known as unpolarized light. The light emitted by the sun, by a lamp or a tube light are all unpolarised light sources. As you can see in the image below, the direction of propagation is constant, but the planes on which the amplitude occurs are changing.

32. What is polarization? Polarized waves are light waves in which the vibrations occur in a single plane. Plane polarized light consists of waves in which the direction of vibration is the same for all waves. In the image above, you can see that a plane polarized light vibrates on only one plane.  The process of transforming unpolarized light into polarized light is known as polarization . The devices like the polarizers you see are used for the polarization of light.

33. Types of Polarization There are two linear components in the electric field of light that are perpendicular to each other such that their amplitudes are equal, but the phase difference is π/2. The propagation of the occurring electric field will be in a circular motion. Linear Polarization In linear polarization, the electric field of light is limited to a single plane along the direction of propagation Circular Polarization Elliptical Polarization The electric field of light follows an elliptical propagation. The amplitude and phase difference between the two linear components are not equal.

34. Methods used in The Polarization of Light Polarization by Transmission Polarization by Reflection Polarization by Scattering Polarization by Refraction

35. Applications of Polarization It is used in sunglasses to reduce the glare. Polaroid filters are used in plastic industries for performing stress analysis tests. Three-dimensional movies are produced and shown with the help of polarization It is used for differentiating between transverse and longitudinal waves . Infrared spectroscopy uses polarization It is used in seismology to study earthquakes In Chemistry, the chirality of organic compounds is tested using polarization techniques

36. What is Doppler Effect? Doppler effect or Doppler shift is a phenomenon that is observed whenever the source of waves is moving with respect to an observer. For example, an ambulance crossing you with its siren blaring is a common physical demonstration of the Doppler Effect . The Doppler effect or the Doppler shift describes the changes in the frequency of any sound or light wave produced by a moving source with respect to an observer . Christian Johann Doppler first proposed the Doppler Effect (Doppler Shift) in 1842.

37. What is Doppler Effect? When the light source moves away from the observer, the frequency received by the observer will be less than the frequency transmitted by the source. This causes a shift towards the red end of the visible light spectrum. Astronomers call it the  redshift . When the light source moves towards the observer, the frequency received by the observer will be greater than the frequency transmitted by the source. This causes a shift towards the high-frequency end of the visible light spectrum. Astronomers call it the  blue shift .

38. Activity : match the concepts Reflection Refraction Prism Diffraction Optics The study of light and its behavior The bending of a wave around an obstacle or through a slit The reflection of light on a polished surface The change in the direction of light when it passes from one medium to another A crystal that separates light into its component colors

39. Online Resources What is Light? https://youtu.be/g4OYz75zZ8w?si=C6HVdOGecD7EerFI Electromagnetic Spectrum https://youtu.be/FrfcjNTapCU?si=ipuK50GUw5hdWMCp Reflection https:// youtu.be/yscrBkfPRyc?si=48LU3eGAufV8crIM Refraction https:// youtu.be/ON1QGqB6vxg?si=Y3n3sGTeH6IiK6bx Snell’s Law - https:// youtu.be/ohQheheySDw?si=pkvmH2enRvt601Es Total Internal Reflection - https:// youtu.be/a20C08qmC_o?si=00jveM7GpaZvnK-R Diffraction https:// youtu.be/9hCrhllI0ck?si=PIe6mMznlRXhAQLM https://youtu.be/gf7j2fumz70?si=8DOqxOwIVyGq_Yl2

40. Online Resources Interference https://youtu.be/xaAthgG0o8o?si=-5jHK9UtPS9x0-6H Polarization https://youtu.be/HH58VmUbOKM?si=8o_OP_RtmIHoNnQg https://youtu.be/E9qpbt0v5Hw?si=T0QJ4pQ9BC1VeRSD https://youtu.be/guqs0uXFpiU?si=zVw8B8cID-lB1M7l https:// youtu.be/PqXRrKHU74s?si=45sAQJINu6-3SlZT Doppler Effect https:// youtu.be/g4OYz75zZ8w?si=C6HVdOGecD7EerFI https://youtu.be/WiTQxNaKAYA?si=W9JO5KHdiSmyJ9eR