4.3d Polarization

THE IB SAYS

Essential idea: All waves can be described by the same sets of mathematical ideas. Detailed knowledge of one area leads to the possibility of prediction in another.

Understandings: Polarization

Applications and skills: Describing methods of polarization; Sketching and interpreting diagrams illustrating polarized, reflected and transmitted beams; Solving problems involving Malus’s law

Guidance: Methods of polarization will be restricted to the use of polarizing filters and reflection from a non-metallic plane surface

Data booklet:

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Polarization

Polarization (or polarisation) is a property of transverse waves only (commonly electromagnetic waves in the IB). If all of the transverse waves in a travelling wave are aligned with the same orientation then the wave is said to be polarized.

In the image below unpolarized waves are incident on a polarizing filter (A - the polarizer). Since the polarizer has a vertical alignment only the vertically aligned light is transmitted. Since all the light has the same orientation it is now called polarized light. This light meets a second polarizing filter (B - called the analyzer) which has the same vertical orientation, so the light is transmitted unchanged. The light then meets another analyzer (C). This has a horizontal orientation, 90˚ to the orientation of the light, so all of it is now blocked.

How can light become polarized?

Polarizing filters can polarize light. Alternatively reflection from many surfaces (such as glass or water) can polarize light at certain angles.

Malus's Law

When polarized light pases through a polarizer (called an analyzer if the light was polarized by a previous polarizing filter) then the amplitude of the transmitted light depends on ø, the angle between the orientation of the polarized light and the orientation of the polarizer / analyzer.

Since the intensity of a wave is proportional to the amplitude squared, the equation above relates intensity of the transmitted wave to the intensity of the original wave and the angle.

Resources from textbooks

Oxford Physics: pages 141 - 144, including multiple worked examples on pages 143 - 144

Hamper HL (2014): page 200

Relevant questions from Dot Point Physics (11 Wave phenomena)

NB: This is in 11. Wave Phenomena as polarization used to be a HL topic. It was also taught in more detail, you no longer need to know about Brewster's Angle, optical activity or how LCD screens work. Ignore these topics.

Pages 107 - 111 have relevant questions, but see comment above.

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