Ohm’s Law -Definition, Statement, Formula, Limitation

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What is Ohm’s Law?

• German physicist and mathematician Georg Simon Ohm discovered that there is a direct proportionality between the potential difference (voltage) applied across a conductor and the resulting electric current. This relationship is called Ohm’s law.

Ohm’s law definition

• Ohm’s law states that the voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions and temperature remain constant.

Ohm’s law formula

• Mathematically, the current and voltage relationship is written as V=IR, Where R is the resistance.

• Three formulas to calculate Current, Voltage, and Resistance:
– V = IR
– I = V / R
– R = V / I

Ohm’s law equation

• Suppose a conductor carries a current I and the potential difference between the two ends of the conductor is V. Then Ohm’s Law states that:

V ∝ I
• The Potential difference is directly proportional to the current in the conductor.

or, V = R I
• Here R is Resistance and, It is constant for the Ohmic conductor.

Explanation of Ohm’s law with diagram

• Suppose a potential difference of 10 volts is applied across a metal wire and a current of 5 amperes flows as a result.

• Now if the potential difference is made 20 volts, the current flow will increase from 5 amperes to 10 amperes. Because of the high potential difference, more electrons flow from one end to the other.

• So the flow of current is directly proportional to the potential difference across the metal conductor.

• This voltage-current relationship was discovered by the German physicist and mathematician Georg Simon Ohm. And the law is called Ohm’s Law.

Circuit Diagram of Ohm’s Law

Ohm's Law Circuit diagram
Ohm’s Law Circuit diagram

Experimental Verification of Ohm’s Law

• Ohm’s Law can be easily verified by an easy and simple experiment.

Instruments Required for this experiment

Voltmeter
Ammeter
Resistor
Rheostat
Battery
Plug Key

Circuit Diagram for this experiment

Ohm's Law
Experimental Verification of Ohm’s Law Circuit

The procedure of the experiment

• Initially, key K is closed and the rheostat is adjusted to obtain minimum readings on ammeter A and voltmeter V.

• Now, slowly increase the current in the circuit using the sliding terminals of the rheostat.

• During the process, the current flowing in the circuit and the corresponding value of the potential difference across the resistance wires are recorded from the ammeter and voltmeter respectively.

• In this way, different sets of current and voltage values are obtained from the ammeter and voltmeter.

• Now, calculate the ratio of V/I. You will notice that the V/I ratio is almost the same in each case. So V/I = R, which is a constant.

• If we plot a graph of current versus potential difference, it will be a straight line. This indicates that the current is proportional to the potential difference.

Ohm’s law graph

Ohm's Law
Ohm’s law graph

Limitations of ohm’s law

• Ohm’s law does not apply to unidirectional electrical components such as diodes and transistors because they allow current to flow in only one direction.

• For non-linear electrical elements with parameters like capacitance, resistance, etc., the ratio of voltage to current will not be constant with respect to time, which makes it difficult to use Ohm’s law.

• So, ohm’s law is not applicable to Insulators, Vacuum tubes, Semiconductors, Transistors, Thermistors, and Filaments of a light bulb.

Calculating Electrical Power Using Ohm’s Law

• Electrical power is the rate at which electrical energy is transferred by an electrical circuit. The unit of power is Watt.

• Electrical power can be calculated by using Ohm’s law and substituting values for voltage, current, and resistance.

Formula of Power

P = V × I
• When the voltage and current values are given.

P = V2 / R
• When the voltage and resistance values are given.

P = I2 R
• When current and resistance values are given.

Power Triangle

• The power triangle can be employed to determine the values of electric power, voltage, and current when the values of the other two parameters are given to us.

• In the power triangle, the power (P) is on the top and current (I) and voltage (V) are at the bottom.

Ohm's Law
Power Triangle

• Power (P) formula for given values of voltage (V) and current (I).
P = VI

• Current (I) formula for given values of voltage (V) and power (P).
♦ I=P/V

• Voltage (V) formula for given values of current (I) and power (P).
V=P/I

Ohm’s Law Matrix Table

• We have 4 parameters which are voltage, current, power, and resistance. In this table, separate equations of 3 parameters are presented, so that we can easily understand what formula we can use to determine the value of a particular parameter.

Ohm's Law
Ohm’s Law Matrix Table

Ohm’s Law Applications

The main applications of Ohm’s law are:

• To determine the voltage, resistance, and current of an electrical circuit.

• To determine the voltage across a resistor in an electrical circuit.

• Ohm’s law maintains the desired voltage drop across the electronic components such as Capacitors, inductors, diodes, diodes, transistors, transistors and oscillators, electromechanical components such as relays and switches, ICs, and connectors.

• Ohm’s law is used in a typical LED circuit to determine the appropriate resistor to safely light the LED.

• Ohm’s law is also used in DC ammeters and other DC shunts to divert current.

Frequently Asked Questions (FAQ)

Q1. What is Ohm’s Law in simple terms?

Answer: The flow of direct current is directly proportional to the potential difference and inversely proportional to the resistance of the circuit.

Q2. Who discovered Ohm’s law?

Answer: Georg Simon Ohm

Q3. What is the unit of resistance?

Answer: Ohm

Q4. What is the formula of resistance?

Answer: R = V ÷ I (Voltage divided by current)

Q5. Why is Ohm’s law important?

Answer: Ohm’s law is very important because it states the relationship between voltage, current, and resistance.


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