LIGHT

A FORM OF ELECTROMAGNETIC RADIATION THAT STIMULATES THE

EYE

I. Electromagnetic RadiationI. Electromagnetic Radiation

A. A. Light is a Light is a wavewave and therefore and therefore has all the properties of waves.has all the properties of waves.

B. Light waves have wavelengths B. Light waves have wavelengths that range from 380nm to 760 nmthat range from 380nm to 760 nm

C. Studying light allows us to study C. Studying light allows us to study all all electromagnetic radiationelectromagnetic radiation

D. D. White lightWhite light is all colors mixed is all colors mixed togethertogether

E. E. Monochromatic lightMonochromatic light is light of is light of one color, a one color, a single wavelengthsingle wavelength or or frequencyfrequency

The numbers listed here are frequenciesnot wavelengths to find the wavelengths Remember v=fλ

II.II. Movement of lightMovement of light

A. Light travels in a A. Light travels in a straight linestraight line

B. The speed of light is B. The speed of light is constantconstant in in a given medium (like the speed of a given medium (like the speed of all waves within a medium)all waves within a medium)

C. Light travels fastest in a C. Light travels fastest in a vacuum vacuum (space)(space)

D. Denoted by the symbol c, found on D. Denoted by the symbol c, found on the table of constants on reference the table of constants on reference tables tables c= 3 X 10c= 3 X 1088 m/s m/s

This refers to all forms of This refers to all forms of electromagnetic electromagnetic radiationradiation not just visible light. not just visible light.

E. Electromagnetic Radiation is produced by E. Electromagnetic Radiation is produced by the movement of charged particlesthe movement of charged particles

F. In a material medium the speed of F. In a material medium the speed of light is always light is always less less than in a than in a vacuum.vacuum.

1. it varies with1. it varies with

a. a. Optical density of the Optical density of the mediummedium

b. b. FrequencyFrequency

G. The speed of light in air is very G. The speed of light in air is very close to the speed of light in a close to the speed of light in a vacuum, The same value is vacuum, The same value is generally used for bothgenerally used for both

III.III. REFLECTIONREFLECTION

A. Law of ReflectionA. Law of Reflection

1. Statement: 1. Statement: When a light When a light ray is incident upon a ray is incident upon a reflecting surface the angle of reflecting surface the angle of incidence is equal to the angle incidence is equal to the angle of reflection.of reflection.

θi = angle of incidence θr angle of reflectionNormal is a line perpendicular to the reflecting surface

B.B. Regular ReflectionRegular Reflection

1. Occurs when light hits a 1. Occurs when light hits a polished surface (flat).polished surface (flat). This is This is when the law of reflection applieswhen the law of reflection applies

2. The reflected rays are all parallel 2. The reflected rays are all parallel because because normalsnormals are parallel are parallel

C.C. Diffuse reflectionDiffuse reflection

1. occurs when light hits an 1. occurs when light hits an irregularirregular surface. surface.

2. The reflected rays are 2. The reflected rays are scattered.scattered. Not parallel because Not parallel because the normals are not parallelthe normals are not parallel

IV.IV. REFRACTIONREFRACTION

A. A. The bending (change in The bending (change in direction)direction) of light as it moves from one of light as it moves from one medium to another.medium to another.

B. The incident ray strikes the B. The incident ray strikes the boundary between two media. boundary between two media. It will It will change direction and speed as it change direction and speed as it enters the new medium. enters the new medium.

C. When the angle of incidence is zero, C. When the angle of incidence is zero, along the normal,along the normal, the ray passes the ray passes straight through into the new medium. straight through into the new medium.

θ1 is the angle the incident ray makes with the normal (line perpendicular to surface)θ2 is the angle the refracted ray makes with the normal

D. D. Optical Density- property of a Optical Density- property of a medium that determines medium that determines the speed the speed of lightof light

1. the more dense the 1. the more dense the slower slower the the light will travel and vice versalight will travel and vice versa

E. The refracted ray will bend E. The refracted ray will bend towardtoward the normal when it enters a more the normal when it enters a more optically dense medium. optically dense medium.

F.F. The refracted ray will bend away The refracted ray will bend away from the normal when it enters from the normal when it enters a a medium that is less optically medium that is less optically densedense. .

Example of light entering a more dense medium. The ray bend toward the normal and slows down

Example of a light ray entering a less dense medium and bends away from the normal and speeds up

G.G. Absolute Index of RefractionAbsolute Index of Refraction

1. More optically dense media have a 1. More optically dense media have a higherhigher index of refraction. index of refraction.

2. Values are 1.00 or greater2. Values are 1.00 or greater

3. represented by 3. represented by nn

4. n=c/v4. n=c/v

n = n = absolute index of refractionabsolute index of refraction

c= c= speed of light in a vacuum, speed of light in a vacuum, 3.0X103.0X1088m/sm/s

v= v= speed of light in a given medium, speed of light in a given medium, m/sm/s

5. Values on Reference Tables5. Values on Reference Tables

H.H. Snell’s LawSnell’s Law

1. Gives the relationship between 1. Gives the relationship between angle of incidence and angles of angle of incidence and angles of refraction to the index of refractionrefraction to the index of refraction

2. n2. n11sinsinθθ11 = = nn22sinsinθθ22

nn1=1= index of refraction of incident index of refraction of incident

mediummedium

nn22 = = index of refraction of refracted index of refraction of refracted

mediummedium

θθ1=1= the angle of incidence the angle of incidence

θθ22 = = the angle of refractionthe angle of refraction

I.I. The relationship between index of The relationship between index of refraction, velocity and wavelength is refraction, velocity and wavelength is given by:given by:

nn22 = = vv11 = = λλ11

nn11 v v22 λλ22

Where 1 represent medium 1 and 2 Where 1 represent medium 1 and 2 represents medium 2represents medium 2

Units v= Units v= velocityvelocity m/sm/s λλ = = wavelengthwavelength,,mm

nn22/n/n11 is called the relative index of is called the relative index of refraction.refraction.

J.J. Critical angleCritical angle

1. Definition- 1. Definition- the measure of the measure of the incident angle that causes the incident angle that causes the refracted ray to lie right the refracted ray to lie right along the boundary between along the boundary between the two mediums.the two mediums.

2. unique to a substance.2. unique to a substance.

3. To calculate, use Snell’s law and 3. To calculate, use Snell’s law and substitute in 90 for the refracted substitute in 90 for the refracted ray. nray. n11sin sin θθ11 = n = n22sin 90sin 90

AS θ1 INCREASES SO DOES θ2, UNTIL IT IS EQUAL TO 90. THEN THEREFRACTED RAY MOVES ALONG THE BOUNDARY OF THE 2 MEDIUMS

K.K. Total internal reflectionTotal internal reflection

1. occurs when the critical angle is 1. occurs when the critical angle is exceeded,exceeded, light can no longer light can no longer escape and is escape and is reflectedreflected back into back into the medium.the medium.

2. Law of reflection applies here2. Law of reflection applies here

V.V. DispersionDispersion

A. As light enters a medium each A. As light enters a medium each wave of different frequency (color) wave of different frequency (color) travels at different travels at different speeds.speeds.

B. When white light falls on a B. When white light falls on a prism, the waves of each prism, the waves of each frequency refract by different frequency refract by different amounts, separating the colors.amounts, separating the colors.

C. C. Red lightRed light refracts the least refracts the least because red light has the highest because red light has the highest velocity in glassvelocity in glass. Violet. Violet the most. the most.

VI.VI. Polarziation of LightPolarziation of Light

A. Def: Separation of a beam of A. Def: Separation of a beam of light so that the light so that the vibrationsvibrations are in are in one plane. one plane.

B. Property of B. Property of transverse waves.transverse waves.

C. C. LightLight can be can be polarizedpolarized so it so it must be a must be a transverse wavetransverse wave..

Doppler and lightDoppler and light

When an object emitting light (like a When an object emitting light (like a star) is moving away from another star) is moving away from another object (like the earth) the object (like the earth) the wavelength of light appears to be wavelength of light appears to be getting longer which means that the getting longer which means that the color of the light is shifted toward the color of the light is shifted toward the red end of the spectrum. This is red end of the spectrum. This is what is meant by red shift. what is meant by red shift. Conversely if an object is moving Conversely if an object is moving toward another then the shift is toward another then the shift is toward the blue end of the spectrum.toward the blue end of the spectrum.