OHMS LAW
In present generation technology has improved a lot, for example we are carrying a mobile phones having so many features such as internet, gaming, video calling & many android applications, there is a equal growth of technology had takes place in electricity, it means compare with the past there are so many methods implemented in analysis of circuits and calculating the unknown parameters.
There are many formulas present in the history of electricity but each and every formula based on the basic position of ohms law.
In 18thcentury a scientist named GEORGE OHM made an experiment on galvanic cells, he investigated galvanic circuit mathematically and published a book named Die galvanic kette and he created a formula which makes the future runs on it. The formula is V=I*R
Where V= potential difference between two points
I= current flowing through the conductor
R= Resistance of the conductor
From the above formula you here the name conductor, the theory of conductors is explained in Electronic Devices session. so, visit this session and clarify your doubts.
The above formula says potential difference , a doubt arises what is potential difference, the answer is in physics we know here are two types energies
1. potential energy
2. kinetic energy
Potential energy means change in the position of the object whereas kinetic energy means motion of the body. In a electric circuit when elements are connected in series the voltage is different but current is same, the difference in voltages arises the potential difference.
To exclaim the ohms law in definition:
OHMS LAW : At constant temparature, the potential difference across the two points of a conductor is directly proportional to the current flowing through the conductor.
V α I
By removing proportionality and keep a proportionality constant.
V = IR
*The unit for resistance is given after the scientist OHM(Ω)
From this formula you observed that voltage is directly proportional to the current i.e. if current in the circuit increases, the voltage also increase and vice versa.
Now you are clear about the ohms law, if a problem is given in the circuit for finding voltage, current, and resistance the below formulas are used.
For finding voltage V=IR
For finding current I=V/R
For finding resistance R=v/I
To understand it in easier way the below figure shows a ohms triangle. This will help you to remember easily.
We have another formula for resistance i.e.
R = ρ* L/A
Where L= Length of the conductor
A= Area of cross section of the conductor
ρ= proportionality constant
Resistance : Resistance is the property of the material which always opposes the flow of current through it.
Resistance mainly depends upon the following factors:
1. It depends on the length of the conductor
2. It depends on the cross sectional area of the conductor.
Here R α L/A
R α L
R α 1/A
It defines that if length of the conductor increases the resistance of the conductor wire increases whereas the area of cross section of the wire decreases.
Now you have a question that what is use of these formulas to know clearly see below:
We have from resistance ohms law R = V/I
Another formula for resistance is R = ρ* L/A
By equating these two formulas & neglecting constants we get
V/I = L/A
From this relation clear that I = A.
It means the current depends upon the area of the conductor, if current requirement is more the size of the conductor should be more. The size of the conductor depending upon the current is manufactured by using gauges.
Resistors are having the property of resistance, in your college labs you will find the resistance. Resistor having the major role in each & every electric circuits, without resistor (or) without resistance there is no electrical appliances, because the only property which can resist the power is resistance due to resistance only the power can be controlled.
You learn that resistor plays a major role hence you have to find the value of resistance, here the question is how to find the value of resistance. The below problem gives the conclusion for it.
EXAMPLE: The electric circuit consist of voltage 10v and current 5amp . Find the resistor value?
Solution: Given
Voltage = 10v
Current = 5amp
Resistor = ?
From ohms law V=I*R
R= V/I =10/5 = 2Ω
The resistor colour codings are given below :
The resistor colour codings are given below :
LIMITATIONS FOR OHMS LAW:
The ohms law has some limitations given below:
1. The ohms law is not applicable for unilateral network
2. It is not applicable to temperature variant circuits
3. It is true for metallic conductors
4. It is not applicable for break down voltages.
Limitation 1: The above limitations are now discuss each one in order, the ohms law is not applicable for unilateral network, the unilateral network means the network which built with unidirectional elements such as diodes & semiconductor devices.
Limitation 2 : Once refer ohms law, At constant temparature, the potential difference across the two points of a conductor is directly proportional to the current flowing through the conductor. Here the temperature should be kept constant so this law is applicable only for dc circuits.
R = ρ*L/A
R = ρo (α(T-To)H)
Where T = Temparature
To = Reference temparature (or) room temperature
Ρo = constant
Limitation 3 : The ohms law obey for the metallic conductors, because the conductors are current carriers in nature so, the current flowing through the conductor is proportional to the potential difference.
Limitation 4 : This law is not applicable for the break down voltages, because these breakdown voltages are occurred in unilateral network components such as diodes &other semiconductor devices.
From the above discussion we know about the ohms law in electric point of view. There are so many views of using ohms law, some of them are listed below:
Ohms law in vector form
V = E*L
ΔV = - ∫E.dl
Where E = Electric field vector
dl= Element of the path.
Ohms law in point form
J =σ*E
Where J = current density = current/ area = I/A
σ= conductivity material
E = Electric field.
The ohms law is useful in so many ways in hydraulic systems & other applications. The great scientist who sponsored a great formula for the electcric world is died in the year 1854. For his greatness a statue is placed at the technical university of munich located at Germany.
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