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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Electrical quantities

Electric charge


  • there are positive and negative charges 
  • unlike charges attract and that like charges repel 
  • charge is measured in coulombs (C)

You can detect an electrostatic charge using a leaf electroscope 
If a charged object is placed near the cap, charges are induced.
The metal cap gets one type of charge (positive or negative) and
the metal stem and gold leaf get the other type of charge so they
repel each other.


  • charging a body involves the addition or removal of electrons 

Electric field: a region in which an electric charge experiences a force
•Conductors: materials that let electrons pass through them. Metals are the best electrical conductors as they have free electrons. This also makes them good thermal conductors
•Insulators: materials that hardly conduct at all. Their electrons are tightly held to atoms and hardly move, but they can be transferred by rubbing

  • direction of an electric field at a point is the direction of the force on a positive charge at that point 

    • an electric field as a region in which an electric charge experiences a force 

      Induced Charge: a charge that “appears” on an uncharged object because of a charged object nearby, for example if a positively charged rod is brought near a small piece of aluminium foil. Electrons in the foil are pulled towards the rod, which leaves the bottom of the foil with a net positive charge. The attraction is stronger than the repulsion because the attracting charges are closer than the repelling ones. 

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