NCERT solutions for classes 12 Physics Electrical Resistance Notes
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In this article, ‘Electrostatic Resistance’ from Class 12th Physics is being discussed.
Resistance: The hindrance offered by a conductor to the flow of current.SI unit of resistance is ohm.The Electrical Resistance of a conductor depends on its length‘l’,cross-sectional area ‘A’ and nature of material and is given by
where ? is the resistivity of the material of the conductor.
Colour code for carbon resistances: Very high resistances are made of carbon. The value of high resistance is specified by four bands of different colors.
The first three bands represent the value of resistance while the last band represents tolerance. The first band represents the first digit, the second band represents the second digit and thethird band represents multiplier in powers of 10. The color of the fourth band tells the tolerance.The absence of thefourth band means a tolerance of 20%.
The following table gives the color code:
For practice sets of Current Electricity & more, click on NCERT Physics Class 12.
To memorize the color codes, the following sentence is of great help:
Ques: Determine the resistance of a resistor with the following colors for the rings:
yellow, red, orange,gold.
Ans: We know numbers for yellow, red, orange, goldis 4,2,3 and 5% respectively.
R = 42×103Ω ±5%
Ques: Determine the resistance of the resistor in the following figure:
Ans: Using table,
Resistance R = 47×102Ω ±5%
Ques: How will you represent a resistance 3700 Ω±10% by color code?
Ans: The value of carbon resistance = 3700 Ω±10%
The color attached to numbers 3,7,2 are orange,violet and red respectively.
For 10% accuracy,the color is silver. Thus the bands of color on carbon resistance in the sequence are orange, violet, red and silver.
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