Polarisation Flashcards
What are the different types of Polarisation
Linear, Circular, Elliptical and unpolarised
What is Irradiance proportional to?
To the average square of the electric field.
What are Polarisation Phenomena about?
The direction and Amplitude of the Electric field.
What does Polarisation describe?
The behaviour of the electric field associated with light
What kind of wave is light in isotrophic materials
A transverse wave
What happens to the direction of the electric field during linear polarisation?
It remains constant
How does a polaroid produce linearly polarised light?
By transmitting the electric vector along the axis of the polaroid and absorbing the perpendicular electric vector.
When does a polaroid placed in front of polarised light transmit the most?
When it is rotated parallel to the direction of polarisation
Can light be partially Polarised
Yes
What are the conditions for linear polarisation?
The direction of the electric field vector remains constant.
What are the conditions for circular polarisation?
The x and y amplitudes of E are equal and there is a phase difference of pi/2 between them.
What are the conditions for elliptical polarisation?
The amplitudes of the electric vector E don’t have to be the same and there doesn’t have to be a specific phase difference between them.
What is the most general case of polarisation and why?
Elliptical polarisation because the amplitudes of don’t have to equal and neither does the phase.
What is unpolarised light?
Consists of light where the electric field varies at random between successive measurements at one point.
What is optical activity?
The ability of a material to rotate the direction of linear polarisation as the light travels through.
What are the different types of optically active materials?
D-Rotatory and L-Rotatory
What direction do D-rotatory materials rotate the polarisation? Give an example of something that is D-rotatory?
Clockwise and Natural sugars
What direction do L-rotatory materials rotate the polarisation? Give an example of something that is L-rotatory?
Anti-Clockwise and Chiral amino acids.
What can circular polarisers be used for?
To enhance the contrast of LED displays. Light from the display passes through the polariser. Background light is transmitted through the polariser but reflects off the display screen causing it to change handedness. This then means that the background light won’t pass back through the polariser and will be absorbed.
What happens in an optically active material?
Light travels through as two circularly polarised rays at slightly different speeds. As there phase difference varies so there direction of linear polarisation also varies.
What kind of molecules is optical activity caused by and what structure do they have?
Chiral molecules with a helical twist.
What are the components of the prism spectrometer?
Prism, Slit, Collimator, Telescope
