James Clerk Maxwell (1831 – 1879)

• In 1865, James Clerk Maxwell showed that light is comprised of both electricity and magnetism.

Electromagnetic (light) Waves

c=fλ

The speed of the light wave remains constant in a given medium.

Radiowaves…not just AM & FM These light waves

are a few cm to several football fields in wavelength

Cordless phones, radios, garage door openers, RC toys.

AM vs FM radio

Frequency Modulated

Amplitude Modulated

• Both AM & FM radio signals have advantages and disadvantages.

• Generally, AM waves have much longer wavelengths than FM waves and can DIFFRACT better than FM waves and can travel greater distances before the signal fades. FM is more direct line of sight.

• However, because information is coded in the amplitude of an AM wave, power lines and lightning can influence the amplitude and are more likely to interfere with the AM wave.

• FM has a greater range of frequency which is better for music whereas AM is better for talk radio since there isn’t much fluctuation in a person’s voice.

Microwaves

Infrared

Infrared picture showing heat loss for a house.

Pit vipers, pythons, and boas possess special organs that form images in the brain of the thermal environment, much like vision occurs in the human brain. Thus, these snakes "see" heat, and this amazing system is the most sensitive infrared detector on Earth, natural or artificial.

BOSTON BOMBER 2013

Visible

Ultraviolet

X-RAYS• In 1895, W.C. Röntgen

discovered mysterious rays capable of passing through the human body.

• Mostly used for medical and industry

Gamma Ray• High-energy photons are emitted as one of

three types of radiation resulting from natural radioactivity. Differs from X-rays where radiation is emitted by excited nuclei rather than electrons

• Gamma ray sources are used for cancer treatment and for diagnostic purposes

• Highest energy EM wave, highest f, shortest wavelength, most penetrating, most damaging of all EM waves

Reflection and Refraction

Rays instead of waves A A rayray of light is an imaginary line drawn of light is an imaginary line drawn

along the direction of travel of the light along the direction of travel of the light beams. We use this instead of a wave.beams. We use this instead of a wave.

Law of Reflection

θi

The normal is a line perpendicular to the surface

Specular Reflection:

Diffuse Reflection:

With diffuse reflection, your eye sees reflected light at all angles. With specular reflection (from a mirror), your eye must be in the correct position.

Which photo demonstratesspecular reflection?

If water was smooth you would just see reflection of object as in picture at left. But the surface is rougher where waves act like an array of flat mirrors reflecting is such a way as shown below. The light then appears smeared into a long vertical column.

Sun & moon reflect in a line

Refraction of LightSame as waves/sound unit. Bending due to a speed change due to material change entering at an angle.

Identify #1-5

θi

θi

θrθr

θi>θr θi<θr

The Index of Refraction

Some Indices of RefractionSome Indices of Refraction

Snell’s Law of Refraction

ExampleExample: : A ray of light is incident on the surface of a block of clear ice (1.309) at an angle of 40.0° with the normal. Part of the light is reflected and part is refracted. Find the angle between the reflected and refracted light.

Example: The light emitted by a helium–neon laser has a wavelength of 632.8nm in air. As the light travels from air into zircon (1.923), finda) its speed in zircon

b) its frequency in zircon

c) its wavelength in zircon.

Illusions from refraction Objects appear ‘bent’ or

disjointed.

Objects appear ‘higher’

Our eye-brain system fools us and we conjure up an image since we cannot follow the path of refraction

Romantic Sunset not really there!? What will I tell my lover!!

Water on the road mirage

“Seeing heat” mirage

Dispersion

Variation of Index of Refraction with Wavelength• Violet light refracts

more than red light when passing from air into a material

Critical Angle

θc

Total Internal ReflectionWhen you exceed θC

Diamonds

 

Fiber Optics and T.I.R..

A bright underwater flood light at the bottom of a 2.75m deep pool is positioned 1.85m from one edge of the pool. At what angle will light emerge from the surface of the water at the edge of the pool with respect to ground. Assume the pool is filled to the brim with water.

light

ground

Image Types for Mirrors

Image characteristics:

A) TYPE –

B) ORIENTATION -

C) MAGNIFICATION (M) -

D) Position & height of image and object -

Reflection & Image Formation by a Plane Mirror

Characteristics of the Image Formed by a Plane/Flat Mirror

Concave Mirror

Parallel light rays reflecting off of concave mirror

Note how all 4 rays reflect and converge at common point. This is called FOCAL POINT.

Focal Length Incoming rays are parallel

and all reflect through a common point called the

The distance from the mirror to the focal point is called the

The focal length is ½ the

radius of curvature f= R/2

Applications of concave mirror:

SATELLITE DISH -

Behind flashlight bulbs, headlights, searchlights.

SOLAR COOKER

Convex Mirror

APPLICATIONS:

RAY DIAGRAMS

Object inside the focal point.

Characteristics of image:

IMAGE IN CONVEX MIRROR

Mirror equationMirror equation

MagnificationMagnification

Sign Convention: Reflective side of mirror is positive & back side of mirror is negative

Negative magnification or hi = inverted image

Example A concave makeup mirror is designed so that a

person 25cm in front of it sees an upright image magnified by a factor of two. What is the radius of curvature of the mirror?

How far from a concave mirror with a focal length of 22.5 cm must an object be placed to produce an image with a magnification of +3.65?

Example2

Thin Lenses

Converging or Convex Lenses (THICKER AT CENTER)

Parallel rays refract through converging lens and then proceed through F on other side.

Diverging or Concave Lenses (THICKER AT EDGES)

Parallel rays refract through diverging lens and then diverge where rays can be traced backwards through F on incident side.

Ray Diagram

Diverging lens

Sign convention for lenses

Where you expect light to end up is assumed positive (opposite side of lens)

Converging lenses have +f

Diverging lenses have -f

Example Based on the picture Based on the picture

shown, describe the shown, describe the type of lens and the type of lens and the type of imagetype of image

If the magnifying glass was immersed in water, If the magnifying glass was immersed in water, what effect (if any) would that have on the what effect (if any) would that have on the rays leaving the lens?rays leaving the lens?

APPLICATIONS OF LENSES• Overhead projector (lens + mirror),

eyeglasses, contacts, magnifying glass, telescopes, microscopes, your eye, etc

Lenses and your EYE

• The ability of the eye to instantly adjust its focal length is known as accommodation.

• Your ciliary muscles flex and manipulate the curvature and shape of your lens which changes the focal length of the lens.

Farsighted

Nearsighted

• Astigmatism means that the cornea is oval like a football instead of spherical like a basketball. This causes light to focus on more than one point in the eye, resulting in blurred vision at a distance or near.

Combinations of Lenses

Combination of Thin Lenses• The image produced by the first lens is calculated

as though the second lens were not present• The light then approaches the second lens as if it

had come from the image of the first lens• The image of the first lens is treated as the object

of the second lens• The image formed by the second lens is the final

image of the system

• If the image formed by the first lens lies on the back side of the second lens, then the image is treated at a virtual object for the second lensdo will be negative – virtual objects CAN form real

images

• The overall magnification is the product of the magnification of the separate lenses

ExampleAn object is located 4.75m from a simple optical system consisting of two converging lenses. The first lens of this system has a focal length of 100mm and the second lens, which is 20.0cm from the first lens, has a focal length of 150.0mm. What is the magnification of the system?

Example 2 An object is placed 20.0cm to the left of a

converging lens of focal length 25.0cm. A diverging lens of focal length 10.0cm is 25.0cm to the right of the converging lens. Find the position and magnification of the final image.