This Physics video tutorial in HINDI is explaining the fundamentals of color code for four colour bands in a carbon resistor. A carbon resistor has four bands A, B, C and D of different colours. The first two bands A and B indicate the first two significant figures of resistance. The third band C indicates the decimal multiplier. The fourth band D indicates the tolerance of the resistor.
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The following table gives the colour code for carbon resistor.
Colour Figure Multiplier Tolerance
Black 0 10^0
Brown 1 10^1
Red 2 10^2
Orange 3 10^3
Yellow 4 10^4
Green 5 10^5 5 %
Blue 6 10^6 2.5 %
Violet 7 10^7 0.1 %
Grey 8 10^8 0.05 %
White 9 10^9
Gold 5 %
Silver 10 %
No colour 20 %
Other relevant topics :
Electric current is defined as the rate of flow of electric charge through a conductor.
In other words, it is defined as the amount of electric charge crossing through any cross-section of a conductor in unit time.
So, electric current, i= q/t
where, q is the total charge flowing through any cross-section in time t.
electric current is a scalar quantity.
In S.I., its unit is ampere (A).
1 ampere = 1 coulomb second-1.
Current density in a conductor is defined as the current flowing through the conductor per unit cross-sectional area of that conductor.
Hence current density,
j = i/A
In vector notation,
(j ) ⃗ = i/A ⃗
Drift velocity :-
The drift velocity is defined as the average velocity with which free electrons in a conductor get drifted under the influence of an external electric field applied across the conductor.
It is a vector quantity.
In S.I., its unit is ms^(-1).
Electron mobility :-
The electron mobility of a conductor is defined as the drift velocity acquired per unit strength of the electric field applied across the conductor.
electron mobility, μ = v_d/E
In S.I., its unit is m2 V-1s-1.
Ohm's law :-
Ohm's law states that the current flowing through a conductor is directly proportional to the potential difference across its two ends, provided that the physical conditions ( temperature, mechanical strain, etc ) remain constant.
V ∝ i
or, V = R i
where, R is constant of proportionality and is called electric resistance of the conductor.
Resistance of a conductor.
Resistance of a conductor is defined as the ratio of the potential difference applied across the conductor to the current flowing through it.
R = V/i
In S.I., its unit is ohm (Ω).
1 ohm = 1 volt ampere-1.
Resistivity of a material :-
Resistivity or specific resistance of a material is defined as the resistance offered by a wire of that material of unit length and unit cross-sectional area.
ρ = R A/l
Conductance of a conductor :-
The reciprocal of resistance of a conductor is called the conductance of that conductor.
Conductance, G = 1/R
In S.I., its unit is mho or ohm-1 (Ω-1) or siemen (S)
Conductivity of a material :-
The reciprocal of resistivity of a material is called the conductivity of that conductor.
Conductivity, σ = 1/ρ
In S.I., its unit is ohm-1 metre-1 (Ω-1 m-1) or mho metre-1 or seimen metre-1(S m-1)
Series combination of resistors :-
Two or more resistors are said to be in connected in series combination, if same current passes through each of them, when some potential difference is applied across the combination.
If R_s is the resistance equivalent to the series combination,
R_s = R_1+ R_2 + R_3 + ....
Parallel combination of resistors :-
Two or more resistors are said to be in connected in parallel combination, if same potential difference is applied across each of them.
If R_p is the resistance equivalent to the parallel combination,
1/R_p = 1/R_1 + 1/R_2 + 1/R_3
Electromotive force :-
The potential difference between the two poles of a cell in an open circuit is called electromotive force of the cell.
It is denoted by E.
In S.I., its unit is volt (V) or joule coulomb-1 ( J C-1 ).
Terminal potential difference of a cell :-
The potential difference between the two poles of a cell in a closed circuit is called terminal potential difference of the cell.
Lost volt :-
The potential drop in a cell due to the internal resistance of the cell is called the lost volt.
Kirchhoff's laws :-
Kirchhoff's first law (junction rule) :- It states that the algebraic sum of the currents meeting at a point in an electric circuit is always zero.
Kirchhoff's first law (loop rule) :- it states that in any part of an electric circuit, the algebraic sum of the e.m.f.s is equal to the algebraic sum of the products of the resistances and currents flowing through them.
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