Physics > Current Electricity > 3.0 Ohm's law
Current Electricity
1.0 Introduction
2.0 Conduction of current in a metal
3.0 Ohm's law
3.1 Temperature dependence of resistance
3.2 Resistivities of different materials
3.3 Limitations of ohm's law
4.0 Combination of Resistors
5.0 Electromotive force $\left( \xi \right)$
6.0 Heating effect of current
7.0 Wheatstone bridge
8.0 Metre Bridge Or Slide wire bridge
9.0 Potentiometer
9.1 Comparison of emfs of two primary cells.
9.2 Determination of Internal resistance of a cell using potentiometer
10.0 Electrical devices
3.2 Resistivities of different materials
3.2 Resistivities of different materials
3.3 Limitations of ohm's law
9.2 Determination of Internal resistance of a cell using potentiometer
| Material | $\rho (\Omega m)$ |
| Silver | $1.47 \times {10^{ - 8}}$ |
| Copper | $1.72 \times {10^{ - 8}}$ |
| Gold | $2.35 \times {10^{ - 8}}$ |
Colour code of carbon resistor
The value of resistors and their percentage accuracy are indicated on carbon resistor by colour code printed on them.
Colour code of carbon resistor is given by
| Colour | Digit | Multiplier | Tolerance |
| Black | 0 | ${10^0}$ | |
| Brown | 1 | ${10^1}$ | 1% |
| Red | 2 | ${10^2}$ | 2% |
| Orange | 3 | ${10^3}$ | |
| Yellow | 4 | ${10^4}$ | |
| Green | 5 | ${10^5}$ | 0.5% |
| Blue | 6 | ${10^6}$ | 0.25% |
| Voilet | 7 | ${10^7}$ | 0.1% |
| Grey | 8 | ${10^8}$ | |
| White | 9 | ${10^9}$ | |
| Gold | ${10^{-1}}$ | 5% | |
| Silver | ${10^{-2}}$ | 10% | |
| (none) | 20% |
Note: The brown, red, green, blue and violet are used as tolerance codes on 5-band resistors only. All 5-band resistor use a colored tolerance band. The blank band which has 20% tolerance is only used for the "4-band" code.
How to find the resistance of the carbon resistor using color codes
Suppose the colours on resistor as shown in the figure are Brown, Yellow, Green and Gold.
So,
Brown will be used as a digit = 1
Yellow will be used as a digit = 4
Green will be used as a multiplier =${10^5}$
Gold will be used as tollerance = 5%
Therefore the resistance is, $$ \Rightarrow 14 \times {10^5}\Omega \quad {\text{with a tolerance of 5% }}$$
