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## Speed, Frequency, Wavelength, energy and propagation

Speed: The speed of EMR in free space always travels the speed of light. Frequency: The number of crests of the wave that pass by a point every second. Frequency= speed / wavelength Wavelength: The distance between crests or troughs. Energy: Sometimes called radiant energy Propagation: This describes how the waves react when they are transmitted.

## Source of all EMR is accelerating charge

When an electric charge accelerates, EMR is produced. Also, any changing magnetic field produces EMR.

## EMR Spectrum

### Relationship/Location of different "bands" of spectrum.

Bands decrease in Frequency and increase in wavelength from left to right.   Bands decrease in Frequency and increase in wavelength from left to right.

### Uses/Examples of various bands

Radio waves used to transmit audio. Microwaves spin water molecules creating heat from friction. Visible band is what we see. X rays penetrates tissue to the bone then creates an image of the bone.

## Interactions with matter (along with which representation best describes interaction and how frequency/wavelength play a role)

### Reflection

This refers to the change in direction of a wavefront at an interface between two different media. Examples include light, sound and water waves.

### Refraction

An optical effect.  As light passes from one transparent medium to another, it changes speed, and bends. How much this happens depends on the refractive index of the mediums and the angle between the light ray and the line perpendicular (normal) to the surface separating the two mediums (medium/medium interface).  Each medium has a different refractive index.  The angle between the light ray and the normal as it leaves a medium is called the angle of incidence. The angle between the light ray and the normal as it enters a medium is called the angle of refraction.

### Dispersion

The phenomenon in which the velocity of a wave depends on its frequency or when the group velocity depends on the frequency. It is sometimes called chromatic dispersion or group-velocity dispersioin.

### Diffraction

This refers to the apparent bending of waves around small objects and the spreading out of waves past small openings.

### Interference

This is also known as wave propagation. It is the superposition of two or more waves that results in a new wave pattern.

### Polarization

This describes the orientation of the oscillations of waves. Is specifies the orientation of the wave’s electric field at a point in space over a period of the oscillation

### Absorption

This is the way that the energy of a photon is taken up by matter.

### Scattering

This refers to a deviation in a, what would have been, straight trajectory of moving particles due to non-uniformities in the a medium.

### Transparent, translucent, and opaque

Transparency allows light to pass through a material. Translucency allows light to pass through diffusely. Opacity is the opposite property of translucency.

### Flourescence

The emission of light by a substance that has absorbed electromagnetic radiation of a different wavelength.

### Phosphorescence

This is kind of like fluorescence but it has a slower re-emition of the radiation that it absorbs.