Ch 2 Optics Contents 1- The Nature of Light 2 Reflection and Refraction 3 The Law of Refraction 4 Total Internal Reflection, Binocular, Optical Fiber 5 Dispersion and Prisms, Color Matching 6 Eye vision September 14, 20151W3

Objectives September 14, 2015W32 1- Understand the nature, origin and sources of light 2-Use the laws of Reflection and Refraction to understand some optical devices 3- Discuss the theory of operation of some medical instruments. 4- Understand light dispersion and the theory of Color Matching

Nature of Light Theories Light was though to be a stream of particles (Corpuscular theory) James Clerk Maxwell ( ) developed the electromagnetic theory and pronounced that light is a form of high frequency electromagnetic wave Max Planck ( ) put forward the quantum theory of light (light is emitted in the form of photons) September 14, 20153W3

What is the light? WavesParticles Is it? Or September 14, 20154W3

Properties of light - two models Light ray model Particle-like view Photons travel in straight lines Applications –Mirrors –Prisms –Lenses Wave model Traces motions of wave fronts Best explains –Interference –Diffraction –Polarization September 14, 20155W3

Light is an electromagnetic wave. The electric (E) and magnetic (B) fields are in phase. The electric field, the magnetic field, and the propagation direction are all perpendicular. September 14, 20156W3

Waves can interfere. September 14, 20157W3

Light is not only a wave, but also a particle. Photographs taken in dimmer light look grainier. When we detect very weak light, we find that it’s made up of particles. We call them photons. September 14, 20158W3

Where does light come from? September 14, 20159W3

Sources of light Accelerating charges emit light 1- Linearly accelerating charge 2-Synchrotron radiation— light emitted by charged particles deflected by a magnetic field 3-Bremsstrahlung (Braking radiation)— light emitted when charged particles collide with other charged particles September 14, W3

4-But the vast majority of light in the universe comes from molecular vibrations emitting light. Electrons vibrate in their motion around nuclei High frequency: ~ cycles per second. Nuclei in molecules vibrate with respect to each other Intermediate frequency: ~ cycles per second. Nuclei in molecules rotate Low frequency: ~ cycles per second. September 14, W3

Polarized and unpolarized media Unpolarized medium Polarized medium On the right, the displacements of the charges are correlated, so it is polarized at any given time (and its polarization is oscillating). Note that matter’s polarization is analogous to the polarization of light. Indeed, it will cause the emission of light with the same polarization direction. September 14, W3

Sources of light Matter constantly emits and absorbs radiation Emission mechanism –Accelerated, oscillating charges produce electromagnetic waves Absorption mechanism –Oscillating electromagnetic waves accelerate charges within matter Different accelerations lead to different frequencies Luminous –Producing light –The Sun versus the nonluminous Moon Incandescent –Glowing with visible light from high temperatures –Examples: flames, incandescent light bulbs September 14, W3

The Interaction of Light and Matter: The interaction of light and matter is what makes life interesting. Everything we see is the result of this interaction. Why is light absorbed or transmitted by a particular medium? Light causes matter to vibrate. Matter in turn emits light, which interferes with the original light. Traces motions of wave fronts Best explains –Interference –Diffraction –Polarization September 14, W3

Light interacts with matter Interaction begins at surface and depends on –Smoothness of surface –Nature of the material –Angle of incidence Possible interactions –Absorption and transmission –Reflection –Refraction September 14, W3

Geometrical Optics: Study of reflection and refraction of light from surfaces using the ray approximation. 1-The ray approximation states that: light travels in straight lines until it is reflected or refracted and then travels in straight lines again. 2-The wavelength of light must be small compared to the size of the objects or else diffractive effects occur. September 14, W3

Reflection details Angles measured with respect to the “surface normal” –Line perpendicular to the surface Law of reflection  i =  r September 14, W3

Light refraction September 14, 2015W318 Experiment shows that the path of a light ray through a refracting surface is reversible. For example, the ray in Figure a travels from point A to point B. If the ray originated at B, it would follow the same path to reach point A, but the reflected ray would be in the glass.

Refraction September 14, W3

The Fundamental Law 11 22 n1n1 n2n2 Snell’s Law September 14, W3 Sin 0=0 Sin 90= 1

n2n2 n1n1 θCθC P θ1θ1 θ1θ1 θ1θ1 θ1θ1 θ2θ2 θ2θ2 Critical Angle September 14, W3

Total internal reflection September 14, 2015W322

Refraction, cont. Critical angle –Light refracted parallel to surface –No light passes through surface - “total internal reflection” –Applications - fiber optics, gemstone brilliance SubstanceIndex of refraction Light speed AirApprox. 1~c Water c Glass c Diamond c BE condensate 18,000,00038 mph! September 14, W3

Optical Instruments Binoculars Many optical instruments, such as binoculars, periscopes, and telescopes, use glass prisms and total internal reflection to turn a beam of light through 90° or 180°. September 14, W3 Assignment Write a short report on Binoculars taking into consideration the following points 1- Optical phenomena 2- Structure

Fiber Optics Light can travel with little loss in a curved optical fiber because the light is totally reflected whenever it strikes the core-cladding interface and because the absorption of light by the core itself is small. September 14, W3

Optical Fiber Structure September 14, 2015W326 ncnc n core n core > n c

Utilizations September 14, 2015W327 Physicians often use fiber-optic cables to aid in the diagnosis and correction of certain medical problems without the intrusion of major surgery. For example, a fiber-optic cable can be threaded through the esophagus and into the stomach to look for ulcers. In this application, the cable consists of two fiber-optic lines: one to transmit a beam of light into the stomach for illumination and the other to allow the light to be transmitted out of the stomach.

Example-Endoscopy In the field of medicine, optical fiber cables have had extraordinary impact. In the practice of endoscopy, for instance, a device called an endoscope is used to peer inside the body. A colonoscope reveals a polyp (red) attached to the wall of the colon. A bronchoscope is being used to look for signs of pulmonary disease. September 14, W3

Arthroscopic Surgery Optical fibers have made arthroscopic surgery possible, such as the repair of a damaged knee shown in this photograph: September 14, W3

Answer the following question Are there applications in dentistry Justify your answer September 14, 2015W330

Light Refraction Here h and h” are heights of the body and its image September 14, 2015W331

Thin Lenses

The magnification of a thin lens is September 14, 2015W333 Combine definition of focal length with lensmaker’s equation If f > 0, we have a converging lens If f < 0, we have a diverging lens What if f = infinity ?

Power of a Lens The power of a lens in diopters is the inverse of its focal length P = 1/f

Exercises Calculate image positions, s i Calculate image heights, h i, for (a) and (b) Calculate image length for (c) Are images real or virtual, upright or inverted, and reduced or enlarged Fig , p. 538

Image Reconstruction (Lens) 1. Rays parallel to the optical axis, go through the focal point. 2. Rays through the focal point, emerge parallel to the optical axis. 3. Rays through the center of a lens or through the center of curvature of a mirror are undeviated. Optical Axis

The eye September 14, 2015W337

Vision September 14, 2015W338 The near point is the closest distance for which the lens can accommodate to focus light on the retina. Typically, the near point of the eye is at age 10 about 18 cm. at age 20 about 25 cm, at age 40, 50 cm at age cm or greater The far point of the eye represents the farthest distance for which the lens of the relaxed eye can focus light on the retina A person with normal vision is able to see very distant objects, such as the Moon, and so has a far point at infinity.

Farsightedness (or hyperopia) September 14, 2015W339

Nearsightedness (or myopia) September 14, 2015W340

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Assignment Write a report, not more than 2 bages about eye vision including the following points 1-lens system of the eye 2-Accomodation 3-Resolving power of the eye 4-Retina structure and function September 14, 2015W343

Dispersion and colors White light –Mixture of colors in sunlight –Separated with a prism Dispersion –Index of refraction varies with wavelength –Different wavelengths refract at different angles –Violet refracted most (blue sky) –Red refracted least (red sunsets) –Example: rainbows Wavelength/frequency related September 14, W3

Dispersion of the refractive index allows prisms to separate white light into its components and to measure the wavelength of light. Dispersion is the tendency of optical properties to depend on wavelength. Dispersion can be good or bad, depending on what you’d like to do. Dispersive element White light Dispersed beam n( ) September 14, W3

Color Matching To understand color you must appreciate the three dimensional nature of color. The dimensions of color are: HUE(color) is commonly referred to as color, E.g. Blue, Orange etc. It is associated with the wavelength of the light received. VALUE (brightness) is how we tell a light hue from a dark one. CHROMA (saturation) is the intensity or saturation of a hue. September 14, 2015W346

Hue -colors September 14, 2015W347

VALUE (brightness) September 14, 2015W348

Saturation September 14, 2015W349

Additive primary colors theory September 14, 2015W350 1 Red+ 1 Blue = M agenta 1 Blue+1 Green = Cyan 1 Green+1 Red=Yellow 1 Red + 1 Blue + 1 Green = White 2 Red+1 Green=Orange 2 Green+1 Red=Lime 1 Blue+1 Green+4 Red=Brown

Important A good site to visit September 14, 2015W351

Assignment Solve the following problems September 14, 2015W352