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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Digital electronics and dangers of electricity

Digital electronics 

Analogue uses a whole range of continuous variations to transmit a signal. Digital signals use only 2 states, on and off. With on and off signals logic gates can be used to manipulate these. Logic gates are processors (manipulate the signals) that are circuits containing transistors and other components. Here are the logic gates that we need to know: 

Dangers of electricity 

Damaged insulation: contact with the wire (live wire especially) due to gap in the insulation causes electric shock which can cause serious injury or shock.
•Overheating of cables: when long extension leads are coiled up, they may overheat. The current warms the wire, but the heat has less area to escape from a tight bundle. This might cause a fire.
•Damp conditions: water can conduct a current, so if electrical equipment is wet someone might get electrocuted YAY! 
Fuses: a thin piece of wire which overheats and melts (the fuse ‘blows’) if the current is too high. It is placed on the live wire before the switch. This prevents overheating and catching fire. A fuse will have a specific current value (e.g. 13A) so when choosing a suitable fuse you must use the one which can have the lowest current value but over the current value of the appliance.
*The plug: 


Circuit breakers: an automatic switch which if the current rises over a specified value, the electromagnet pulls the contacts apart, breaking the circuit. The reset button is to rest everything. It works like a fuse but is better because it can be reset.

Benefits of earthing metal 





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