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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 is Ohm's law. This is also called a fundamental law of electricity. It gives therelationship between basic electrical quantities. These basic quantities are current, resistance, and voltage.

We know that resistance is the opposite force which restricts the flow of electricity. The voltage is the electromotive force which is the reason for the movement of electrons and this is the cause of flow of electric current which is measured in ampere. What is the relation between these three main quantities? How they are connected with each other? How the reduction in one quantity can affect the other? All these questions are answered by Ohm. Let s discuss about this law and its applications. What is Ohm's Law?Back to TopOhm's law states that :"the Current through the conductor is directly proportional to the potential difference across its ends provided the temperature remains constant."Consider a conductor across which voltage is appliedOhm's Law

Current starts flowing through a conductor, We can also express Current in terms of Voltage and Resistance asV = 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. Thisis due to the fact that the resistance offered by the point at low potential point is less and hence current gets easy path to flow.Ohm's Law FormulaBack to Topwe 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 ohm s 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 ohm s law current equation.

In terms of Resistance it is expressed as

R = VI We will call this ohm s law resistance equation.Ohm's Law PowerBack to TopOhms law states the relationship between three basic quantities of the electriccircuit namely Voltage, Current and Resistance.

Ohms law can be stated as:V = IRwhere V = Voltage,I = Current,R = Resistance.

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Ohms Law Watts :The Units of Power is joule per second (J/s) or watts. The Watts gives the relationship between of these quantities with the power applied to the electrical appliance connected in the electrical circuit. The ohm's law and watts law can be combined together to form a pie chart using which we can find any of the four quantities namely

Power Voltage Current and Resistance of the circuit.

In the below figure see the relation between these quantities in the form of circle.Ohm's WheelThis 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 equationsgiven in the upper left half of the circle.2. For finding the current we can use upper right half of the circle and depending 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 lower half of the circle.

Ohm's Law CircleBack to TopOhms law gives idea between relation of Voltage current and Resistance in a simple 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 findany variable just hide the letter associated with it and see which two quantities are remaining and the relation between them.

If we want to find voltage V, hide the V in the circle, the remaining quantities 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 quantities are V and R and there is the horizontal line in between so the current canbe find by dividing the V by R. If we want to find resistance R, hide the R in the circle, the remaining quantities are V and I and there is the horizontal line in between so the resistance 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 figure is known as ohms law triangle.

Ohm's Law ExperimentBack to TopTo perform the validity of the ohms law we can perform experiment and analyse th

e results obtained in the experiment.Ohms Law CircuitApparatus 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

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hand from minimum position to the maximum position in the steps of constant increase 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 GraphOhm's Law ProblemsBack to TopLets now discuss some problems to understand the ohm s law:

Solved ExamplesQuestion 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 = VRI = 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 applied to the electric iron?Solution: Voltage equation is given by V = I RHere, 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 Current flowing through the halogen light is 5 A. Find the resistance of the Halogen light?Solution: given V = 110 V, I = 5 AThe Resistance is given by R = VIR = 1105,R = 22 OSo, the Resistance of Halogen light is 22 ?.