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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Current

Current 

Current: a flow of charge, the SI unit is the Ampere (A).
•An ammeter measures the current in a circuit. It is connected in series, the current is a rate of flow of charge.
Charge (C) = current (A) x time (s) C = Ix t 


A digital ammeter is a device that is inserted in a circuit to measure electrical current in amperes (A). Some models are powered by electricity, but most are battery operated and can be used for measurements done outdoors. Like an analog ammeter, a digital ammeter should have a very low resistance so that the characteristic of the circuit under test will not be changed when the digital ammeter is inserted.


  • current in metals is due to a flow of electrons 

    Electromotive force

    •The maximum voltage a cell can produce is called the electromotive force (EMF), measured in volts. When a current is being supplied, the voltage is lower because of the energy wastage inside the cell. A cell produces its maximum PD when not in a circuit and not supplying current. 




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