engineering

Polaroid (polarizer)

Polaroid (polarizer) is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Polaroid (polarizer) rather than just read about it. In short: Polaroid is a type of synthetic plastic sheet which is used as a polarizer or polarizing filter. A trademark of the Polaroid Corporation, the term has since entered common use.

Key takeaways

Polaroid (polarizer) belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Polaroid (polarizer) to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Polaroid (polarizer) from memory before moving on to harder problems.

Reference excerpt

Polaroid is a type of synthetic plastic sheet which is used as a polarizer or polarizing filter. A trademark of the Polaroid Corporation, the term has since entered common use.

Patent The original material, patented in 1929 and further developed in 1932 by Edwin H. Land, consists of many microscopic crystals of iodoquinine sulphate (herapathite) embedded in a transparent nitrocellulose polymer film. The needle-like crystals are aligned during the manufacture of the film by stretching or by applying electric or magnetic fields. With the crystals aligned, the sheet is dichroic: it tends to absorb light which is polarized parallel to the direction of crystal alignment but to transmit light which is polarized perpendicular to it. The resultant electric field of an electromagnetic wave (such as light) determines its polarization. If the wave interacts with a line of crystals as in a sheet of polaroid, any varying electric field in the direction parallel to the line of the crystals will cause a current to flow along this line. The electrons moving in this current will collide with other particles and re-emit the light backwards and forwards. This will cancel the incident wave causing little or no transmission through the sheet. The component of the electric field perpendicular to the line of crystals, however, can cause only small movements in the electrons as they cannot move very much from side to side. This means there will be little change in the perpendicular component of the field leading to transmission of the part of the light wave polarized perpendicular to the crystals only, hence allowing the material to be used as a light polarizer.

This material, known as J-sheet, was later replaced by the improved H-sheet Polaroid, invented in 1938 by Land. H-sheet is a polyvinyl alcohol (PVA) polymer impregnated with iodine. During manufacture, the PVA polymer chains are stretched such that they form an array of aligned, linear molecules in the material. The iodine dopant attaches to the PVA molecules and makes them conducting along the length of the chains. Light polarized parallel to the chains is absorbed, and light polarized perpendicular to the chains is transmitted. Another type of Polaroid is the K-sheet polarizer, which consists of aligned polyvinylene chains in a PVA polymer created by dehydrating PVA. This polarizer material is particularly resistant to humidity and heat.

Applications Polarizing sheets are used in liquid-crystal displays, optical microscopes and sunglasses. Since Polaroid sheet is dichroic, it will absorb impinging light of one plane of polarization, so sunglasses will reduce the partially polarized light reflected from level surfaces such as windows and sheets of water, for example. They are also used to examine for chain orientation in transparent plastic products made from polystyrene or polycarbonate. The intensity of light passing through a Polaroid polarizer is described by Malus' law.

References

Edwin H. Land (1951). "Some aspects on the development of sheet polarizers". Journal of the Optical Society of America 41(12): 957–963. Halliday, Resnick, Walker. Fundamentals of Physics, 7th edition, John Wiley & Sons William Shurcliff (1962). Polarized Light: Production and Use, Harvard University Press.

External links "One-Way Glass Stops Glare" Popular Mechanics, April 1936 pp. 481-483

Worked examples

Example 1 — a first encounter with Polaroid (polarizer)

Start with the simplest possible case. Write down what Polaroid (polarizer) claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Polaroid (polarizer) before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Polaroid (polarizer) ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Polaroid (polarizer)

In research: Polaroid (polarizer) appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Polaroid (polarizer) in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Polaroid (polarizer) is common in secondary-school and first-year university syllabi. It links to neighbouring topics Brand name materials, Optical materials, Polarization (waves), so understanding it makes those chapters shorter.
In everyday life: Look for Polaroid (polarizer) outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Polaroid (polarizer) in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Polaroid (polarizer) means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Polaroid (polarizer) out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Polaroid (polarizer) in simple terms?

Polaroid is a type of synthetic plastic sheet which is used as a polarizer or polarizing filter. A trademark of the Polaroid Corporation, the term has since entered common use.

Why does Polaroid (polarizer) matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Polaroid (polarizer)?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Polaroid (polarizer).