Measurements

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1.general physics  1.1 length and time  -i-Physical Quantity Physical Quantities A physical quantity is a property of an object that can be measured with a measuring instrument. A physical quantity is usually expressed as “a magnitude ( numerical value)  and a  physical unit or more ” Example :- Normal body temperature of a healthy human being is  37  0 C -ii-Length Measuring Length. Length is “the distance between two points in a space”. According to SI units, the length quantity is expressed in meter. There are several kinds of measuring devices used to measure quantity of length, among others, are as follows. Tools used… a-   Measuring tape. b-   Ruler c-   Vernier callipers. d-    Micrometer Measurement of length Length is measured accurately through many meth...
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Light

Reflection of light


Refraction of light













Critical angle: the angle at which the refracted ray is parallel to the surface of the material. If the angle of incidence is greater than the critical angle there is no refracted ray, there is total internal reflection. If the angle of incidence is less than the critical angle the incidence ray will split into a refracted ray and a weaker reflected ray. 


Refractive index = speed of light in vacuum / speed of light in medium

Refractive index = sin i / sin r
When the incidence angle is equal to the critical angle, the angle of refraction is 90° (parallel to the surface). Since
sin90° equals 1, then a ray coming the other way (the arrow is inverted) would have an angle of incidence of 90° and an angle of refraction of c. If we apply Snell’s law:
n = sin90° / sinc
Sin (critical angle) = 1 / n Critical angle = sin-1(1/n) 

The converging lens




Optical fibres: light put in at one end is totally internally reflected until it comes out the other end. This is used in communications where signals are coded and sent along the fibre as pulses of laser light, and in medicine: an endoscope, an instrument used by surgeons to look inside the body. It contains a long bundle of optic fibres.

Dispersion of light

light of a single frequency is described as monochromatic






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