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 methods. Here are some: Method Notes Ruler Used to make simple measurements accurate to  0.1 cm  (1 mm) Vernier caliper Used to make simple measurements accurate to
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Electromagnetic spectrum

Electromagnetic spectrum 

All electromagnetic waves:
-are produced by particles oscillating or losing energy in some way 
-are transverse waves
-do not need a medium to travel through i.e. can travel through a vacuum -can transfer energy 

speed of electromagnetic waves in a vacuum is 3.0 × 108 m/s and is approximately the same in air 



Uses:
Radio waves – radio and television communications
Microwaves – satellite television and telephones
Infrared – electrical appliances (radiant heaters and grills), remote controllers for televisions and intruder alarms X-rays – medicine (x-ray photography and killing cancer cells) and security
•Safety issues:
X-rays – is a mutagen, it cause cancer (mutations)
Microwaves – cause internal heating of body tissues
•Monochromatic: light of a single wavelength and colour (used in lasers)

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