Definitions [3]
What is a Polaroid?
A Polaroid is a material which polarises light. The phenomenon of selective absorption is made use of in the construction of polariods. There are different types of polaroids.
A Polaroid consists of micro crystals of herapathite (an iodosulphate of quinine). Each crystal is a doubly refracting medium, which absorbs the ordinary ray and transmits only the extra ordinary ray. The modern polaroid consists of a large number of ultra microscopic crystals of herapathite embedded with their optic axes, parallel, in a matrix of nitro - cellulose.
Recently, new types of polariod are prepared in which thin film of polyvinyl alcohol is used. These are colourless crystals which transmit more light, and give better polarisation.
Answer the following question in detail.
Define and describe the magnifying power of an optical instrument.
Angular magnification or magnifying power of an optical instrument is defined as the ratio of the visual angle made by the image formed by that optical instrument (β) to the visual angle subtended by the object when kept at the least distance of distinct vision (α).
Define the term ‘resolving power of a telescope’.
The resolving power of an astronomical telescope is defined as the reciprocal of the smallest angular separation between two point objects whose images can just be resolved by the telescope.
R.P = `(1.22 lambda)/D`
Resolving power is the ability of the telescope to distinguish clearly between two points whose angular separation is less than the smallest angle that the observer’s eye can resolve.
Theorems and Laws [1]
State the law of refraction.
The law of refraction is called Snell’s law.
Snell’s law states that,
- The incident ray, refracted ray and normal to the refracting surface are all coplanar (i.e., lie in the same plane).
- The ratio of the angle of incidence i in the first medium to the angle of reflection r in the second medium is equal to the ratio of the refractive index of the second medium n2 to that of the refractive index of the first medium n1.
`(sin "i")/(sin "r") = "n"_2/"n"_1`
Concepts [13]
- Theories on Light
- Wave Nature of Light
- Huygens' Principle
- Proof of Laws of Reflection and Refraction Using Huygens' Principle
- Interference
- Diffraction of Light
- Polarisation
- Optical Instruments
- Simple Microscope or a Reading Glass
- Compound Microscope
- Telescope
- Optical Instruments: Spectrometer
- Optical Instruments: the Eye
