Electromagnetic waves

Electromagnetic spectrum & Speed of light

Electromagnetic Waves

Light waves are electromagnetic wavesLight waves consist of periodically

changing electric and magnetic fieldsProduced by accelerating charged

particles

The Electromagnetic Spectrum

The complete range of frequencies and wavelengths of EM waves

Visible light is only a small portion of the spectrum

Various kinds are classified according to the methods by which they are generated or received


Radio waves are produced by charges accelerating in a wireMicrowaves are used in radar systems in air-traffic control, for transmitting long distance phone communications in outer space, and to cook food


Infrared waves appear as heat when absorbed by objectsVisible light is produced by the rearrangement of electrons in atoms and molecules•(λ)400-700nm VL human eye can detect


The ozone layer of the atmosphere filters practically all of the high frequency components of the UV radiation

The inner atmosphere readily transmits the remaining lower frequency UV radiation


X rays are used as diagnostic tools by Physicians, but can destroy living tissues and organismsGamma rays are emitted by

radioactive nuclei


c represents the speed of lightc = 3.00x108

The speed of light in a material is always less than c

v=fλ applies to light waves

Speed of Light

Nature and Propagation of Light

The nature of light; Reflection and Refraction; Total Internal Reflection; Dispersion; Polarization; Scattering of Light

Light as a wave•Rectilinear propagation •Can be reflected•Can be refracted

Photoelectric effect•Particle behavior•Increased intensity increases number of electrons emitted

Light: Particle or Wave?

The ability of things to light•Bioluminescence

Anything that can give off its own light•Luminous object

An object that can be seen because of a luminous object• Illuminated object

The facts of Light

The rate at which light is emitted from a source •Luminous flux (P) measured in lumen (lm)

Illumination on a surface•Illuminance, (E) measured in lm/m2 or lux (lx)

The facts of Light

1m

2m

3m

1

1/9

1/4

S

Visible light

Reflection & Refraction

Wave changes direction upon hitting a reflecting surface

Reflection

0ri

R

N

I

R= reflecting rayr= angle of reflectionI= incident rayi= angle of incidenceN= normal

θi= θr

States that waves are reflected from the boundary of the medium at the same angle at which they strike it

Law of Reflection

Wave changes direction upon entering a medium of different density

Refraction

n is the ratio of the speed of light in a vacuum, c, to the speed of light in a material medium, vn=c/v

Absolute index of Refraction

n2= v1= λ1

n1 v2 λ2

The ratio of the sines of the angles, where both angles are measured from the normal to the surface, is equal to the inverse ratio of the two indexes of refraction

Snell’s law/ law of refraction

sinθ2= n1

sinθ1 n2

Index of refraction and the wave aspects of light

λ=λ0/n

f

Frequency of the wave does not change when passing from

one material to another

λ

The wavelength of the wave is different in general in different

materials

As the λ gets shorter, the v decreases

As the λ gets longer, the v increases

Total internal reflection

When does total internal reflection occur? What are

the conditions?

Total Internal Reflection


When light emerges into a

less dense medium, rays

bend away from the normal

As incident rays become more

oblique, angle of refraction

approaches a maximum of 90°


The angle of incidence for

which the refracted ray

emerges tangent to the surface is called critical

angle

The incident angle when θr is

90° (θcrit)

If θr is beyond 90°, then no refracted ray would exist. TIR

occurs


sin θ crit = nb/na

Critical angle for TIR

TIR occurs only when a ray is incident on the interface with a

second material whose n is smaller than that of the material in which

the ray is travelling

If θincidence ≥ θcritical


Electromagnetic waves

Education

Transcript of Electromagnetic waves