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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Potential difference and resistance

Potential difference 

I Potential Difference
•Potential difference, or PD for short, is also known as voltage. Voltage is the amount of energy the cell gives the electrons it pushes out. Voltage is measured in volts (V) and is measured by a voltmeter (connected in parallel). If a cell has 1 Volt, it delivers 1 Joule of energy to each coulomb of charge (J/C).
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Voltage = Energy / Charge Volts = Joules / Coulomb V=E/C 

Analog voltmeter

Digital voltmeter 

Resistance 

  • resistance = p.d./current and understand qualitatively how changes in p.d. or resistance affect current 

    Resistance (Ω) = potential difference (V) / current (A) 
    R = V /I 
    •Factors affecting resistance:
    -    Length
    Double the length = double the resistance (proportional)
    -    Cross-sectional area
    Half the cross-sectional area = double the resistance (inversely proportional) -Material
    Better conductor = less resistance
    -    Temperature
    For metal conductors higher temperature = more resistance
    For semi-metal conductors higher temperature = less resistance
    The V =IR law can be investigated with the following apparatus 


    • Sketch and explain the current-voltage characteristic of an ohmic resistor and a filament lamp








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