ElectroMagnetic Radiation SpectrumThe basics about light and waves

Breakdown:

1.) Terms to Know

2.) What is the E.M.R. Spectrum?

3.) How does light travel?

4.) Characteristics of a wave and light

Terms to know:1.) Radiation - process of emitting radiant energy (light) in the forms of

waves and particles

2.) Electron - subatomic particle of atoms with a negative charge and the

least mass; usually found orbiting the nucleus

3.) Magnetic fields - lines of force that connect the positive and negative

areas of a magnetic body

4.) Waves - movement of energy through a medium or empty space in the

pattern of a sine wave

5.) Spectrum - a continuous sequence or range; in this case, the

wavelengths of light

The E.M. Spectrum- The Electromagnetic spectrum is the full range of wavelengths that light can travel in

The E.M. Spectrum

- light, or radiation, travels at a constant speed in a vacuum

c = ~300,000 km / s

- there are many different types of light, but they all share the same speed

Visible, Ultraviolet (UV), Infrared (IR), X-rays, Microwaves,

Gamma Rays, and Radio Waves

How does light travel?- Light, depending on how you study it, can have the properties of waves or particles

o The EM spectrum breaks down the types of light based on wavelength so we will focus on waves

* Light is special in that its waves do not require a medium to travel through

ex: there is no sound in the vacuum of space because there is no matter for it to travel through

Waves- 2 types of waves:

Transverse and Longitudinal

- Even though matter may be moving (up, down, and all around), it does not travel with the waves, only energy is being passed along. This is true with all waves.

- Wavelength = distance between two crests or two troughs

(in the case of longitudinal waves, the distance between

two areas of compression) measured in SI units (meters)

Longitudinal Waves

•Waves that travel parallel to the direction of motion

•Made up of compressions and rarefactions in the medium that they are traveling in

•Examples: sound waves and s waves for earthquakes

Transverse Waves

•Waves that travel perpendicular to the direction of

displacement

Examples: Light, p wavesfor earthquakes, Ocean waves

*Misconception- As you should have seen, Radio Waves are a type of light and therefore are not sound.Sound waves = Radio waves !

- You may ask: But I hear sound from my

radio, how is this possible?

- Because of the nature of light, sound information can be encoded in Radio waves and later extrapolated back out as sound

.... how this is done is a topic for another time

Characteristics of a Wave

There are 4 basic components to any transverse wave such as light:

1.Amplitude2.Frequency3.Phase4.Polarization

1.) Amplitude- Amplitude is the total displacement of a wave.

o In simple terms, it is the distance from the middle of a wave to its peak

2.) Frequency

- Number of crests (or wavelengths) passing by per second

- Measured in Hertz (Hz), meaning cycles per second

- Equals the inverse of the time it takes for one wavelength to pass by:

f = 1 / t

- Phase is the initial angle of a sinusoidal function at its origin

- If two waves are the same or similar in phase, they will add together

- If they offset enough, they will subtract

3.) Phase

4.) Polarization- Polarization is the orientation of oscillations in the plane perpendicular to a transverse wave's direction of travel

o Different polarizations are cause by the electric and magnetic fields being out of phase from one another

- Possible Polarizations:1.horizontal2.vertical3.circular4.elliptical

Other properties of light:

Because of lights characteristics and physical nature, light has some other interesting properties:

● Diffraction● Refraction● Scattering

Diffraction of Light:

Diffraction of light is the “interference” of its waves when it encounters an opening or an obstacle.

- Seen when the obstacle or opening

matches up closely with the waves wavelength- Longer wavelengths get diffracted more than shorter wavelengths

Diffraction of Light: (cont.) The effects of diffraction are most “easily” examined via the single-slit and double-slit experiments

Based on the size of slits used in comparison to the wavelengths of light, different patterns of interference result

1 x

5 x

Refraction of Light:

Refraction is the bending, or change in direction of light as it passes from one medium to another

- The secondary medium has a different

refractive index from the first

Refraction of Light: (cont.)

If you have ever looked at an object underwater from above, you have witnessed refraction. Because light gets bent as it changes mediums from the air to the water, the image you see becomes “distorted.”

Refraction of Light: (cont. x 2)- A prism works based on this concept. As light enters a prism, the light gets bent as it passes from one medium to the other. -Prisms take it a step further and bent each wavelength of light differently

● This spreads the light out into a rainbow of color as you may have seen.

o The shorter wavelengths bend more than the longer.

Scattering of Light:

Light scattering is the deflection of an incident beam of light off any irregular portion of the medium in which it is passing through.

● Light scatters off of any surface generally speaking, and the type of light being scattered, or reflected, is the color in which you see.

Why is the sky blue?

The atmosphere is a collection of gases that is, for the most part, evenly distributed. As light passes through it, light randomly strikes small particles and molecules suspended in the air column. Because of this, light gets scattered in all directions.

● Shorter wavelengths are more easily scattered, so blue light gets scattered more.

What about dusk and dawn...You may notice when the sun rises and sets, the sky is no longer “blue” but instead more of a yellow/red hue. During these times, sunlight enters the atmosphere at a more extreme angle and must pass through more atmosphere to reach your eyes. By this time, all or most of the shorter wavelengths have been scattered leaving only the longer wavelengths.

If shorter wavelengths scatter more easily...Then why isn’t the sky violet?

- There just isn’t enough violet light

being emitted from the Sun. The sun

because of its temperature gives off

much more blue light therefore it is

more prevalent.