Ohm's Law Formula: Limitations & Applications

Ohm's Law formula is V = IR where V=voltage, I=current, and R=resistance. Ohm’s Law links voltage (V) and current (I) to the properties of the conductor, that is its resistance (r) in a circuit. Ohm’s law states that voltage across a conductor is proportional to the current flowing through it, considering all physical conditions and temperatures remain constant. The most basic and important law of electric circuits is the Ohm's Law.

Key Terms: Ohm's Law, Ohm's law formula, Ohm's Law, Resistance, Ohm's Law Example, Law of Resistance, Ohm's Law Calculation, Voltage, Current

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Ohm’s Law

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Ohms law essentially describes a mathematical relationship between the voltage (V), current (I), and circuit resistance ( R ). 

Ohm's Law

Mathematically, Ohm's Law is written as:

V = I * R

Where, 

• V is the Voltage (Potential Difference) measured in Volts. 

To find voltage (V),

[V = I x R] V(volts) = (amps) x R(Ω)

• It is the current flowing through the conductor.

To Find the current (I),

[I = V / R] I(amps) = V(volts) + R(Ω)

• R is the resistance of the circuit measured in Ohms (Ω).

To find the resistance (R), 

[R = V / I] R= V volts) / I(amps)

Ohms Law Explained 

Ohms law video

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Application of Ohm's Law

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The applications of ohm’s law are:

• Ohm’s law helps in determining resistance, current, voltage of a circuit when two of the three quantities are known to us. 
• Ohms law makes power calculation simple.
• Maintains the desired voltage in the electric component.
• Ohm's law is used in DC shunts and DC ammeter to divert the current.

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Relationship Between Voltage, Resistance and current

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The relationship of current, resistance and voltage is expressed by Ohm’s Law. It states that the current flowing in a circuit is proportional to the applied voltage and inversely proportional to the circuit, provided the temperature remains constant.

Current (I) = Voltage (V) / Resistance (R)

To increase the current flowing in a circuit, the voltage must be increased, or the resistance decreased.

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Calculating Resistance Equation using Ohm’s Law

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Ohm's Law equation is used to calculate the voltage, current and resistance of a circuit. The ohm's law formula triangle is-

Ohms Law Triangle

Now, To calculate the current in a circuit, rearrange the Ohm's Law equation as-

I = V / R

Similarly, you can calculate the electrical resistance of a circuit through-

R = V / I

For a circuit to obey Ohm's Law, Constant Resistance (R) is required.The Electrical resistance in a circuit is affected by various physical factors, including temperature. The resistance increases as the temperature increases (such as copper wire), so Ohm's Law does not hold true in that case.

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Limitations of Ohm’s Law

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Given below are the few examples where the Ohm’s law fails to apply: 

1. A diode demonstrates the limitations of Ohm’s law. When the V vs I graph for a diode is plotted, it is observed that the relation between V and I is not linear. This happens when V is marked in a reverse direction so that the magnitude is fixed. The I is therefore produced in the opposite direction with a different magnitude.
2. Due to the unilateral network, Ohm’s law is not applicable to a water volt-ammeter.
3. It is also not necessary that all the conductors obey Ohm’s law. Also, semiconductors like Germanium and Silicon do not obey Ohm’s law. Therefore, they are regarded as Non-Ohmic conductors.

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Ohm's Law Pie Chart and Matrix Table

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All the equations used to find the current, voltage , resistance and power, and combine them into a simple Ohm’s pie chart and matrix table as shown below.

Ohm's law Pie Chart

We can also combine the individual Ohm’s Law equations into a simple matrix table as shown below for calculating an unknown value.

Ohm’s Law Matrix Table

Discover about the Chapter video:

Current Electricity Detailed Video Explanation:

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Things To Remember

• The Ohm's law helps in determining resistance, current, voltage of a circuit when two of the three quantities are known to us. 
• One of the most important laws in electrical theory as It links voltage (V) and current (I) to the properties of the conductor, that is its resistance (r) in a circuit.
• The SI unit of electric resistance is the ohm (Ω). 1 Ω = 1 V/A.
• Ohm’s law is not applicable to a water volt-ammeter due to the Unilateral Network.

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Previous Year Questions

1. A square loop ABCD, carrying a current I, is placed near and coplanar with a long straight conductor XY carrying a current I, as shown in figure. The net force on the loop will be
2. Which of the following graph represents the variation of resistivity $(\rho)$ with temperature (T) for copper ?​
3. In a good conductor of electricity, the type of bonding that exists is:​
4. A wire of length ll and resistance RR is stretched to get the radius of cross-section r2r2 . Then the new value of RR is​
5. A galvanometer of resistance 20Ω20Ω is to be converted into an ammeter of range 1A1A. If a current of 1mA1mA produces full scale deflection, the shunt required for the purpose is​
6. A current of 5A5A is passing through a metallic wire of cross-sectional area 4×10−6m24×10−6m2 . If the density of charge carriers of the wire is 5×10265×1026 m−3,m−3, the drift velocity of the electrons will be​
7. In the Wheatstone's network given, P=10Ω,Q=20Ω,R=15Ω,S=30Ω,P=10Ω,Q=20Ω,R=15Ω,S=30Ω, the current passing through the battery (of negligible internal resistance) is​
8. An electric motor runs on DC source of emf 200V200V and draws a current of 10A10A. If the efficiency be 40%40%, then the resistance of armature is​
9. An electron moves in a circle of radius 1.0cm1.0cm with a constant speed of 4.0×106m/s4.0×106m/s , the electric current at a point on the circle will be (e=1.6×10−19C)​
10. A cell of constant emf first connected to a resistance $ {{R}_{1}} $ and then connected to a resistance $ {{R}_{2}} $ . If power delivered in both cases is same, then the internal resistance of the cell is​
11. A galvanometer of 50Ω50Ω resistance has 2525 divisions. A current of 4×10−44×10−4 A gives a deflection of one division. To convert this galvanometer into a voltmeter having a range of 25V25V, it should be connected with a resistance of​
12. Five equal resistances each of resistance RR are connected as shown in the figure. A battery of VV volts is connected between AA and BB. The current flowing in AFCEBAFCEB will be​
13. A 6V6V battery is connected to the terminals of a three metre long wire of uniform thickness and resistance of 100Ω100Ω . The difference of potential between two points on the wire separated by a distance of 50cm50cm will be​
14. Which of the following II- VV graph represents ohmic conductors ?​
15. Which of the following is correct for VV-II graph of a good conductor ?​
16. Which of the following is NOT the name of a secondary cell ?​
17. Which of the following is secondary cell?​
18. Wire bound resistors are made by​
19. With increase in temperature the conductivity of​