Light and OpticsLight and Optics

Chapter 22, 23Chapter 22, 23

Light as an Electromagnetic waveLight as an Electromagnetic wave

Light exhibits behaviors which are Light exhibits behaviors which are characteristic of both waves and particlescharacteristic of both waves and particles Interference, Doppler effectInterference, Doppler effect

Electromagnetic waves are waves of Electromagnetic waves are waves of changing electrical and magnetic fields. changing electrical and magnetic fields. A changing electrical field will produce a A changing electrical field will produce a

magnetic field.magnetic field. They travel at 3.00*10They travel at 3.00*1088 m/s m/s First detected by creating a rapidly moving First detected by creating a rapidly moving

electrical charge and detecting the magnetic electrical charge and detecting the magnetic field a distance away by using a loop of wire. field a distance away by using a loop of wire.

Electromagnetic spectrumElectromagnetic spectrum

Electromagnetic waves can be produced Electromagnetic waves can be produced over a wide range of frequenciesover a wide range of frequencies

Other EM waves:Other EM waves: Radio, microwaves, infrared, ultraviolet, Radio, microwaves, infrared, ultraviolet,

x-raysx-rays

PracticePractice

Calculate the wavelength of a 60Hz EM wave, Calculate the wavelength of a 60Hz EM wave, a 93.3 MHz FM radio wave, and a visible red a 93.3 MHz FM radio wave, and a visible red laser of 4.74*10laser of 4.74*101414 HZ HZ

5.0*105.0*1066m, 3.22m, 6.33*10m, 3.22m, 6.33*10-7-7mm

Speed of lightSpeed of light

First attempted by Galileo using mirrorsFirst attempted by Galileo using mirrors Ole Roemer used the period of a moon in Ole Roemer used the period of a moon in

Jupiter's Orbit to prove the speed of light Jupiter's Orbit to prove the speed of light was finite. was finite.

Albert Michelson Used a rotating mirror Albert Michelson Used a rotating mirror and light source to finally prove light and light source to finally prove light moves at a speed of 2.9979*10moves at a speed of 2.9979*1088m/s or m/s or 3.00*103.00*1088 m/s. m/s.

The ray Model of lightThe ray Model of light

Light travels in …Light travels in … Straight linesStraight lines

The straight line paths that light travel in are The straight line paths that light travel in are called called RaysRays

Light travels in every direction from the Light travels in every direction from the source.source.

Geometric optics-describing aspects of light Geometric optics-describing aspects of light by using the ray modelby using the ray model

See smartbook notsSee smartbook nots

RefractionRefraction

Index of RefractionIndex of Refraction Light travels at c = 3.00 *10 Light travels at c = 3.00 *10 88 m/s in a vacuum m/s in a vacuum The speed decreases as it passes through The speed decreases as it passes through

other substances. other substances. The ratio between the speed of light in a The ratio between the speed of light in a

vacuum and the speed of light in another vacuum and the speed of light in another substance is called the index of refractionsubstance is called the index of refraction

n = c / vn = c / v The higher the index, the slower light is The higher the index, the slower light is

travelingtraveling

Refraction Refraction Refraction is the bending of lightRefraction is the bending of light Light bends toward the normal when passing into Light bends toward the normal when passing into

a more dense medium (higher n value)a more dense medium (higher n value) Light bends away the normal when passing into a Light bends away the normal when passing into a

less dense medium (lower n value)less dense medium (lower n value)

Light bends more as the angle of incidence Light bends more as the angle of incidence increases. increases.

Angle of incidence is often written as Θ1

Angle of refraction is often written as Θ2

Snell’s LawSnell’s Law

The angle of refraction depends on the The angle of refraction depends on the speed of light in the two media and the speed of light in the two media and the angle of incidenceangle of incidence

nn11 (sin (sin ΘΘ11) = ) = nn22 (sin (sin ΘΘ22)) (Snell’s Law)(Snell’s Law) Known as the law of refractionKnown as the law of refraction

ExampleExample Light strikes a flat piece of glass at an incident angle of Light strikes a flat piece of glass at an incident angle of

60.0 60.0 oo . In the index of refraction of the glass is 1.50 . In the index of refraction of the glass is 1.50 What is the angle of refraction in the glass, and at what What is the angle of refraction in the glass, and at what angle does the ray emerge from the glass?angle does the ray emerge from the glass?

Total internal ReflectionTotal internal Reflection

When light passes from a more dense When light passes from a more dense material to less dense material, at a material to less dense material, at a particular incident angle the light will skim particular incident angle the light will skim across the surface.across the surface. This angle is the critical angleThis angle is the critical angle Sin Sin ΘΘcc = = nn2 2 / / nn11

For any incident angle greater than this, For any incident angle greater than this, no light is refracted and there is total no light is refracted and there is total internal reflection. internal reflection.

Total internal ReflectionTotal internal Reflection Many optical instruments such as Many optical instruments such as

binoculars use total internal reflection.binoculars use total internal reflection. Prisms are used to reflect lightPrisms are used to reflect light Better than using mirrors because less light is Better than using mirrors because less light is

lost. lost. Fiber optics- glass or plastic fibers that Fiber optics- glass or plastic fibers that

internally reflect light to transmit it from internally reflect light to transmit it from one place to another. one place to another. TelecomunicationsTelecomunications MedicalMedical

• Bronchoscope Bronchoscope

Physics of DiamondsPhysics of Diamonds

Diamonds achieve their brilliance partially from total internal reflection. Because diamonds have a high index of refraction (about 2.3), the critical angle for the total internal reflection is only about 25 degrees. Incident light therefore strikes many of the internal surfaces before it strikes one less than 25 degrees and emerges. After many such reflections, the colors in the light are separated, and seen individually.