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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Properties of waves

General wave properties 

  • waves transfer energy without transferring matter 


    •Wavefront: the peak of a transverse wave or the compression of a longitudinal wave
    •Speed: how fast the wave travels measured in m/s
    •Frequency: the number of waves passing any point per second measured in hertz (Hz), given by this formula:
    Frequency = 1 / period
     Wavelength: the distance between a point on one wave (e.g. the trough) to the equivalent point on the next wave in meters e.g. from crest to crest or compression to compression
    •Amplitude: the maximum distance a wave moves from its rest position when a wave passes
    •Period: the time taken for one oscillation in seconds 



    Transverse waves (e.g. light waves) have oscillations at right-angles to the direction of travel, where as in longitudinal waves the oscillations are in the direction of travel. Transverse waves have crests (peaks) and troughs; where as longitudinal waves (e.g. sound waves) have compressions and rarefactions. 



    When a wave strikes a smooth plane (flat) surface it may be reflected / refracted (bent) or absorbed or any combination of these. An important application of the total reflection off a plane surface is summarised in the law of reflection. 

    The law of reflection

    This says that the angle of incidence i (measured from the normal at the surface) is equal to the angle of reflection r (again measured from the normal to the surface). This law is vital for the success of communication technologies using reflected emr waves (see later). This is shown in the graphics below. 
    In each case i = r
    Water waves travel faster on thesurface of deep water
    than they do on shallow water.
    The change in speed of the wavewill cause refraction
    as shown in the picture below.

    As you can see, the change in speed has changedthe direction of the wave. The slower wavein the shallow water has a smaller wavelength.
    The amount of refractionincreasesas the change in speed of the wave increases.

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