Wave Properties of Light Karolina H. Czarnecka, PhD Department of Molecular Bases of Medicine

Transcription

1 Wave Properties of Light Karolina H. Czarnecka, PhD Department of Molecular Bases of Medicine

2 THE ELECTROMAGNETIC FORCE One of the four fundamental forces, the electromagnetic force manifests itself through the forces between charges (Coulomb's Law) and the magnetic force, both of which are summarized in the Lorentz force law. Fundamentally, both magnetic and electric forces are manifestations of an exchange force involving the exchange of photons.

3 THE ELECTROMAGNETIC FORCE both magnetic and electric forces are manifestations of an exchange force involving the exchange of photons. Lorentz Force Law The electric force is straightforward, being in the direction of the electric field if the charge q is positive, but the direction of the magnetic part of the force is given by the right hand rule.

4 Electromagnetic Radiation and the Wave Particle Duality Energy can travel through a vacuum or matter as electromagnetic radiation. Electromagnetic radiation is a transverse wave with magnetic and electric components that oscillate perpendicular to each other. The electromagnetic spectrum is the range of all possible wavelengths and frequencies of electromagnetic radiation including visible light.

5 Wave Properties of Light General Properties of Light General Properties of Waves Reflection Refraction Dispersion Diffraction Interference Young's Double Slit Experiment Phase Change on Reflection Students are supposed to read from the textbook chapter: 21

6 General Properties of Light In vacuum light always travels at the same speed: c = 3.0 x 10 8 m/s. Until the middle of the 1800's, the generally accepted theory of light was the particle picture. In this viewpoint, advocated by Newton, light was considered to be a stream of tiny particles. However, in the late 1800's, the particle picture was replaced by the wave theory of light. This was because certain phenomena associated with light, namely refraction, diffraction and interference, could only be explained using the wave picture.

7 Visible light one particular type of electromagnetic radiation. Other types of electromagnetic radiation include radio waves, infrared radiation (heat), ultraviolet radiation, x-rays and -rays.

8 Gamma rays not only from decays typically have frequencies above 10 exahertz (or >1019 Hz), and energies above 100 kev and wavelengths less than 10 picometers (10 11 m), which is less than the diameter of an atom Electromagnetic radiation from radioactive decay of atomic nuclei is referred to as "gamma rays" no matter its energy, so that there is no lower limit to gamma energy derived from radioactive decay. This radiation commonly has energy of a few hundred kev, and almost always less than 10 MeV.

9 Gamma rays In astronomy, gamma rays are defined by their energy, and no production process needs to be specified. The energies of gamma rays from astronomical sources range to over 10 TeV, an energy far too large to result from radioactive decay. A notable example is the extremely powerful bursts of high-energy radiation referred to as long duration gamma-ray bursts, of energies higher than can be produced by radioactive decay. These bursts of gamma rays, thought to be due to the collapse of stars called hypernovae, are the most powerful events so far discovered in the cosmos.

10 Electromagnetic radiation that can be detected by the human eye. It extends from a wavelength of about 780 nm ( m) at the red end of the spectrum to one of 380 nm (violet light). Visible light spans the divide between infrared and ultraviolet radiation.

11 Gamma rays the shortest, but not the lowest frequency in the EM spectrum. Gamma photons travel at the speed of light.

12 General properties of waves - defintions The wavelength ( λ) is the distance between neighbouring crests or troughs. The speed ( v ) is the rate at which the crests (or troughs) move forward. The Period ( T ) is the time that elapses between passing crests. The period can be expressed in terms of the speed and wavelength: T = λ /v The frequency ( f ) is the number of crests (or troughs) that pass by per unit time. It is equal to the inverse of the period: f = 1/T Using the expression for T above we get the useful expression: v = f λ

13 Which of the following waves is used most in telecommunications? Radio waves. Infrared. Ultraviolet. Microwaves. Which of the following kinds of waves is most commonly used to cook food? Visible Light. Infrared. Microwaves. Gamma rays Which of the following kinds of electromagnetic waves has the HIGHEST energy? Radio waves. Visible light. Microwaves. X-rays.

14 Which of the following waves is used most in telecommunications? Radio waves. Infrared. Ultraviolet. Microwaves. Which of the following kinds of waves is most commonly used to cook food? Visible Light. Infrared. Microwaves. Gamma rays Which of the following kinds of electromagnetic waves has the HIGHEST energy? Radio waves. Visible light. Microwaves. X-rays.

15 1.The electromagnetic radiation of a wavelength is called sound light kinetics 2. Energy emitted in the form of a wave as a result of the movement of electric charges is horsepower electromagnetic radiation hydroelectric energy 3. Electromagnetic waves need matter to move. 4. Humans can see all light waves. 5. Gamma rays have the lowest frequency in the EM spectrum. 6. Gamma photons travel at the speed of sound. 7. Higher-energy electromagnetic waves have lower frequencies.

16 1.The electromagnetic radiation of a wavelength is called sound light kinetics 2. Energy emitted in the form of a wave as a result of the movement of electric charges is horsepower electromagnetic radiation hydroelectric energy 3. Electromagnetic waves need matter to move. False True 4. Humans can see all light waves. False True 5. Gamma rays have the lowest frequency in the EM spectrum. False True 6. Gamma photons travel at the speed of sound. False True 7. Higher-energy electromagnetic waves have lower frequencies. False True

17 Period T = λ /v frequency f = 1/T Changing the equation: T=1/f => T=T λ /v= 1/f λ = v/f v= λ/f speed= wavelength frequency

18 1. The frequencies of gamma rays are a) higher than 1019 hertz. b) lower than a billion waves per second. c) higher than the frequencies of X rays. d) two of the above 2.Sources of gamma rays include a) the sun. b) collapsing stars. c) radioactive decay. d) all of the above 3. True or false: Gamma rays from space are absorbed by Earth s atmosphere. 5. What is a gamma ray burst? 6. Gamma rays can pass through a) bones. b) teeth. c) skin. d) all of the above 7. Gamma rays can be used to treat. 8. How can gamma rays harm living things? 4. How can gamma rays harm living things?

19 a. Which region of the electromagnetic spectrum has the highest frequency? b. Which region of the electromagnetic spectrum has the longest wavelength? c. Which region of the electromagnetic spectrum will travel with the fastest speed?

20 a. Which region of the electromagnetic spectrum has the highest frequency? b. Which region of the electromagnetic spectrum has the longest wavelength? c. Which region of the electromagnetic spectrum will travel with the fastest speed? a. The gamma radiation region have the highest frequency. b. The radio wave region has the longest wavelength. c. All regions have the same speed. The speed of a wave is not dependent upon its frequency and wavelength but rather upon the properties of the medium through which it travels.

21 e. Which color of the visible light spectrum has the greatest frequency? f. Which color of the visible light spectrum has the greatest wavelength?

22 e. Which color of the visible light spectrum has the greatest frequency? Violet waves have the highest frequencies. f. Which color of the visible light spectrum has the greatest wavelength? Red waves have the longest wavelengths.

23 Reflection The first property of light we consider is reflection from a surface, such as that of a mirror. The two laws of reflection are as follows: 1. The incidenct ray, the reflected ray, and the normal to the reflecting interface at the point of incidence all lie in the same plane. 2. The angle of incidence equals the angle of reflection.

24 camera obscura

25 How the reflected ray goes to the retina?

26 Refraction an effect of wave properties of light conservation of energy and conservation of momentum Due to change of medium, the phase velocity of the wave is changed but its frequency remains constant. The change in direction of propagation of a wave due to a change in its transmission medium.

27 Refraction in water Applies to the situation when the light is transmitted in the medium, not reflected This is most commonly observed when a wave passes from one medium to another at any angle other than 0 from the normal. The straw or pen appears to be broken because of the difference between the angle at which light from it strikes the vertical edge of the glass/water container versus the horizontal surface of the water.

28 Refraction in a Perspex (acrylic) block The refleted ray Source of light

29 Dispersion Dispersion results from different frequencies of light having different velocities. ttps://en.wikipedia.org/wiki/beer%e2%80%93lambert_law

30 Dispersion vs refraction In practice, all materials that refract light will disperse it to some degree. All dispersive materials will refract light. The key difference between the two is that dispersion is referring to the frequency dependence (which is the ability to separate different colors of light) while refraction is referring to the bending of light in a material.

31 Beer Lambert law relates the attenuation of light to the properties of the material through which the light is traveling. The law is commonly applied to chemical analysis measurements and used in understanding attenuation in physical optics, for photons, neutrons or rarefied gases. ttps://en.wikipedia.org/wiki/beer%e2%80%93lambert_law

32 Transmittance Transmittance of the surface of a material is its effectiveness in transmitting radiant energy. It is the fraction of incident electromagnetic power that is transmitted through a sample, the transmission coefficient, is the ratio of the transmitted to incident electric field "Beer lambert1" by CarlosRC - Wikipedia. Licensed under Public Domain via Wikipedia -

33 An example of Beer Lambert law: green laser light in a solution of Rhodamine 6B. The beam radiant power becomes weaker as it passes through solution ttps://en.wikipedia.org/wiki/beer%e2%80%93lambert_law

34 Absorbance absorbance is the common logarithm of the ratio of incident to transmitted radiant power through a material, spectral absorbance the common logarithm of the ratio of incident to transmitted spectral radiant power through a material.

35 Transmittance to absorbance relation The absorbance of a solution is a measure of how much light it absorbs. ttps://en.wikipedia.org/wiki/beer%e2%80%93lambert_law

36 Transmittance to absorbance relation If you shine 100 units of light in and get 90 out you have a transmittance of 90/100, 90%. You can calculate absorbance as: Absorbance= -log (%Transmittance)

37 Absorbance vs wavelenght

38 Absorbance of X-rays -> density Radiographic density is the measure of overall darkening of the image. Density is a logarithmic unit that describes the ratio between light hitting the film and light being transmitted through the film. A higher radiographic density represents more opaque areas of the film, and lower density more transparent areas of the film. ico.jpg/250px-aire_subdiafragm%c3%a1tico.jpg

39 X-ray attenuation the primary beam passes through the body, some of the radiation is absorbed in a process known as attenuation. Anatomy that is denser has a higher rate of attenuation -> bone will absorb more x-rays than soft tissue. What remains of the primary beam after attenuation is known as the remnant beam. The remnant beam is responsible for exposing the image receptor. Areas on the image receptor that receive the most radiation (portions of the remnant beam experiencing the least attenuation) will be more heavily exposed, and therefore will be processed as being darker m4wqbu1g137065/gw134h364

40 Diffraction interference effect of waves according to the Huygens Fresnel principle These characteristic behaviors are exhibited when a wave encounters an obstacle or a slit that is comparable in size to its wavelength. Similar effects occur when a light wave travels through a medium with a varying refractive index, or when a sound wave travels through a medium with varying acoustic impedance.

41 Diffraction occurs with all waves, including sound waves, water waves, and electromagnetic waves such as visible light, X-rays and radio waves. When waves reach a narrow slit, the water in the slit vibrates like a point source. The waves thus sent out from secondary sources along the slit are nearly in-phase when arriving any point in the forward direction. The diffracted wave resembles a circular wave with centre at the slit.

42 ttps://en.wikipedia.org/wiki/beer%e2%80%93lambert_law Interference

43 ttps://en.wikipedia.org/wiki/beer%e2%80%93lambert_law Moire a stripes

44 stereoscopy 1. Images must be made from 2 positions arranged so that the casting rays extending from the nearest points intersect at an angle less than 150 degrees. 2. Both photos should be made on a similar scale, is not a difference of more than 15% ttps://en.wikipedia.org/wiki/beer%e2%80%93lambert_law

45 ttps://en.wikipedia.org/wiki/beer%e2%80%93lambert_law

46 Is there a difference between these images?

47 Is there a difference between these images?

48 The effect of the imposition of two images - 3D images

49 Quantum Theory This solved the black-body problem and was consistent with the observed experimental data. Despite the advances that he and others made using this idea, interestingly, Planck remained quite skeptical of quantized energy for many years. He insisted that the calculations that he had done, and the conclusions that he had reached, were somehow a sophisticated mathematical trick and that ultimately the old, classical model would prevail.

50 Double-slit experiment a demonstration that light and matter can display characteristics of both classically defined waves and particles

51 phase change on reflection

52

53 Why are some objects transparent? Some light passes through them All light passes through them No light passes through them Why does light refract? Its size changes Its speed changes Its shape changes Which travels most quickly? Water waves Sound waves Light waves The angle of incidence always equals what? The angle of reflection The angle of dispersion The angle of exodus Which of these colours is not found in the spectrum? Cyan Yellow Green What are the three primary colours in light? Red, green and yellow Red, green and blue Red, blue and yellow

54 Why are some objects transparent? Some light passes through them All light passes through them No light passes through them Why does light refract? Its size changes Its speed changes Its shape changes Which travels most quickly? Water waves Sound waves Light waves The angle of incidence always equals what? The angle of reflection The angle of dispersion The angle of exodus Which of these colours is not found in the spectrum? Cyan Yellow Green What are the three primary colours in light? Red, green and yellow Red, green and blue Red, blue and yellow