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Ohm's Law

The electricity is the flow of charges from positive to negative or vice-versa.

It is also said the flow of electrons. The one of important law of electricity i
s Ohm's law. This is also called a fundamental law of electricity. It gives the
relationship between basic electrical quantities. These basic quantities are cur
rent, resistance, and voltage.
We know that resistance is the opposite force which restricts the flow of electr
icity. The voltage is the electromotive force which is the reason for the moveme
nt of electrons and this is the cause of flow of electric current which is measu
red in ampere. What is the relation between these three main quantities? How the
y are connected with each other? How the reduction in one quantity can affect th
e other? All these questions are answered by Ohm. Lets discuss about this law and
its applications.

What is Ohm's Law?
Ohm's law states that :
"the Current through the conductor is directly proportional to the potential dif
ference across its ends provided the temperature remains constant."Consider a co
nductor across which voltage is applied
Ohm's Law
Current starts flowing through a conductor, We can also express Current in terms
of Voltage and Resistance as
V = IRwhere, V= Voltage applied to the conductor,
R = Resistance of the conductor,
I = Current flowing through the metal conductor.
The Electric Current flows from high potential to the low potential point. This
is due to the fact that the resistance offered by the point at low potential poi
nt is less and hence current gets easy path to flow.
Ohm's Law Formula
we know that when Voltage is applied across any conductor its Voltage increases.
I a V
But every Conductor offers some resistance so Current can be expressed as:
I = VR where,
R is the constant of proportionality and is known as the resistance of the given
conductor,
V = potential difference across the ends,
I = current in the Conductor.
The ohms law is the relation between three variables Voltage (V), Current (I) and
Resistance (R).
We can rewrite above equation in two different equations as;
V=IRWe will call this ohms law current equation.
In terms of Resistance it is expressed as
R = VI We will call this ohms law resistance equation.
Ohm's Law Power
Ohms law states the relationship between three basic quantities of the electric
circuit namely Voltage, Current and Resistance.
Ohms law can be stated as:
V = IRwhere V = Voltage,
I = Current,
R = Resistance.
Ohms Law Watts :
The Units of Power is joule per second (J/s) or watts. The Watts gives the relat
ionship between of these quantities with the power applied to the electrical app
liance connected in the electrical circuit. The ohm's law and watts law can be c
ombined together to form a pie chart using which we can find any of the four qua
ntities namely
Power
Voltage
Current and
Resistance of the circuit.
In the below figure see the relation between these quantities in the form of cir
cle.
Ohm's Wheel
This circle is known as Ohms Law Pie Chart or Ohms Law Chart or Ohms Law Wheel.
1. Using this chart we can find the power we can use any of the three equations
given in the upper left half of the circle.
2. For finding the current we can use upper right half of the circle and dependi
ng upon the given variable we can find the value of the current in the circuit.
3. Similarly we can find the voltage and the resistance using the appropriate lo
wer half of the circle.
Ohm's Law Circle
Ohms law gives idea between relation of Voltage current and Resistance in a simp
le way:
Ohm's Law Circle
The letter below the horizontal line in the circle can be considered as division
and the vertical line is considered as the multiplication. So, we want to find
any variable just hide the letter associated with it and see which two quantitie
s are remaining and the relation between them.
If we want to find voltage V, hide the V in the circle, the remaining quanti
ties are I and R and there is the vertical line in between so the voltage can be
find by multiplying the I and R.
If we want to find current I, hide the I in the circle, the remaining quanti
ties are V and R and there is the horizontal line in between so the current can
be find by dividing the V by R.
If we want to find resistance R, hide the R in the circle, the remaining qua
ntities are V and I and there is the horizontal line in between so the resistanc
e can be obtained by dividing the V by I. Although the above diagram is shown as
a circle, we can use the triangle instead of the circle and the resulting figur
e is known as ohms law triangle.
Ohm's Law Experiment
To perform the validity of the ohms law we can perform experiment and analyse th
e results obtained in the experiment.
Ohms Law Circuit
Apparatus required: Rheostat, Ammeter, Voltmeter, Voltage supply of 5V D.C.
Steps of the experiment:
Connect the variable voltage supply to both the ends of the rheostat.
Connect the ammeter in series of the rheostat.
Connect the voltmeter in parallel of the rheostat.
Now, start measuring the voltage and current as you move the rheostat moving
hand from minimum position to the maximum position in the steps of constant inc
rease in current.
Now with this data plot a graph between the voltage and the current.
What do you observe from it.
The graph (see below) between voltage and current is linear that is there is
constant decrease in current when the rheostat is moved from minimum resistance
position to the maximum resistance position.
Ohms Law Graph
Ohm's Law Problems
Lets now discuss some problems to understand the ohms law:
Solved Examples
Question 1: A 10 V battery is connected to the electric bulb of resistance of 20
ohms. Find the current flowing through the electric bulb?
Solution:

Here V= 10 V
R = 20 O
The current flowing through the electric bulb is given by,
I = VR
I = 1020
I = 0.5 amperes.
So, the current flowing through the bulb is 0.5 amperes.

Question 2: A electric iron of resistance 40 O is connected to a supply voltage.
The current flowing through the electric iron is 6 Amperes. Find the voltage ap
plied to the electric iron?
Solution:

Voltage equation is given by V = I R
Here, I = 6 A, R = 40 O
So, Voltage is expressed as V = 6 40,
V = 240 Volts.

Question 3: A 110 V voltage source supplies power to a halogen light. The Curren
t flowing through the halogen light is 5 A. Find the resistance of the Halogen l
ight?
Solution:

given V = 110 V, I = 5 A
The Resistance is given by R = VI
R = 1105,
R = 22 O
So, the Resistance of Halogen light is 22 ?.
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