Superconductors
When few metals are cooled , then below a certain critical temperature their electrical resistance suddenly becomes zero . In this state , these substances are called superconductors and this phenomena is called superconductivity .
Mercury become superconductor at 4.2 K , lead at 7.25 K and niobium at 9.2 K
Colour Coding of Carbon Resistors
The resistance of a carbon resistor can be calculated by the code given on it in the form of coloured strips .
Colour coding Colour Figure Black 0 Brown 1 Red 2 Orange 3 Yellow 4 Green 5 Blue 6 Violet 7 Grey 8 White 9
Tolerance power
Colour Tolerance Gold 5 % Silver 10 % No colour 20 %
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