# Physics: Week 32

This week in the Ron Paul Curriculum physics course was about the wave nature of light.
This was the last week of the course! The next 4 weeks are going to be spent in review.

Diffraction:

This occurs when waves pass through a narrow opening or around an object.  The amount of diffraction depends on the size of the object, opening, and the wavelength.
The smaller the wave length is to the object, the less diffraction.
Different wavelengths are diffracted at different angles.

Constructive interference:

At some angles, when two waves pass through two little holes, they join constructively.

Destructive interference:

At certain angles, when two waves pass through two little holes, they join destructively.

Fringe patterns:

Colour and wavelength:

White light is a collection of all the colours of the rainbow, with red and violet on the ends.
Red light has a wavelength of 700 nm
Violet light has a wavelength of 400 nm

Dispersion:

The spreading of white light into its visible spectrum.  This can be done with refraction because different wavelengths have different refractive indices.
A prism is a good example.

A point source:

Allows light to come at an object from only one direction.

Diffraction grating:

A diffraction grate has a large number of equally spaced slits or light to pass through.  The slits can be in the thousands of lines per cm.  This is used to precisely measure wavelength.

Spectrometer:

A device for measuring wavelengths, which can also be used for identifying atoms.

Interference by thin films:

In a thin film, light is reflected from the top and bottom of the film.  The two reflected waves can interact constructively or destructively.
If the wavelengths are in phase, they interfere constructively.
If out of phase by 180 degrees, they interfere destructively causing that position to be dark for that wavelength.

Reflection:

This occurs when a wave comes into a new substance that is of a higher index of refraction.  The reflected wave is 180 degrees from what it was originally.