james clerk maxwell (1831 – 1879). electromagnetic (light) waves

James Clerk Maxwell (1831 – 1879)

Electromagnetic (light) Waves

Radio…not just AM & FM

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

Thermogram

We radiate infrared light aka “heat”

Visible

Ultraviolet

X-RAYS

Gamma Ray

Reflection and RefractionReflection and Refraction

of Lightof Light

Rays instead of waves Rays instead of waves approximationapproximation

• 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 ReflectionLaw of Reflection

θi θr

2 types of reflection:2 types of 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.

Refraction of LightRefraction of LightWhen a ray of light enters a different medium at an angle other than 0o with the normal, it will bend or REFRACT due to a speed change due to material change.

θiθi

θr

θr

θi>θr θi<θr

The Index of RefractionThe Index of Refraction

Snell’s Law of Refraction

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

Frequency Between MediaFrequency Between Media

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), find

a) its speed in zircona) its speed in zirconb) its frequency inb) its frequency in zirconzirconc) its wavelength in zircon.c) its wavelength in zircon.

Illusions from refractionIllusions from refraction

Sunset not really there?Sunset not really there?

MirageMirage

DispersionDispersion

Variation of Index of Refraction with Variation of Index of Refraction with WavelengthWavelength

Critical AngleCritical Angle

Total Internal ReflectionTotal Internal Reflection

TIR and ‘bling bling’

Fiber Optics and TIRFiber Optics and TIR

• Plastic or glass rods Plastic or glass rods are used to “pipe” are used to “pipe” light from one place to light from one place to anotheranother

• This ‘light’ can be This ‘light’ can be used to carry used to carry information at light information at light speedspeed

• Fiber Optics, Medical Fiber Optics, Medical EndoscopesEndoscopes

The RainbowThe Rainbow

Observing the RainbowObserving the Rainbow

• If a raindrop high in the sky is observed, the red ray is seenIf a raindrop high in the sky is observed, the red ray is seen• A drop lower in the sky would direct violet light to the observerA drop lower in the sky would direct violet light to the observer• The other colors of the spectra lie in between the red and the The other colors of the spectra lie in between the red and the

violetviolet

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

MIRRORS

Image Types for MirrorsImage 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

What you see when you look into a plane (flat) mirror is an image, which appears to be behind the mirror.

Properties of the Image Formed by a Plane/Flat Mirror

Concave Mirror

Converges light rays after reflection

Parallel light rays reflecting off of Parallel light rays reflecting off of concave mirrorconcave 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 FOCAL POINT, F.

Applications of concave mirrorPARABOLIC REFLECTORS -• Behind flashlight bulbs,

headlights, searchlights. projects light out in a concentrated beam…bulb is placed at focal pt.

• SATELLITE DISH -• Microwaves strike dish and

reflect and collect at the receiver (at focal point)

• SOLAR COOKER• MAKEUP MIRROR…

provides an enlarged image of face when held close to face

Convex MirrorConvex Mirror

Diverges light rays after reflection

APPLICATIONS:

RAY DIAGRAMS

Object inside the focal point.

Characteristics of image:

IMAGE IN CONVEX MIRROR

Mirror equationMirror equation

MagnificationMagnification

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

Use same formulas as mirrors, except that f ≠ R/2…doesn’t apply

Converging or Convex Lenses The difference

between mirrors and lenses is that mirrors reflect and lenses refract light.

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

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 100 mm and the second lens, which is 20.0 cm from the first lens, has a focal length of 150.0 mm. What is the magnification of the system?

Example 2

An object is placed 20.0 cm to the left of a converging lens of focal length 25.0 cm. A diverging lens of focal length 10.0 cm is 25.0 cm to the right of the converging lens. Find the position and magnification of the final image.