Most Repeated NEET Physics Formula: Ohm’s Law

Ohm’s Law (V = IR) has remained a high-yield topic for NEET and other medical examinations. Whether it is simple one-step calculations or complex circuits with multiple loops, the physics part is incomplete without this law. It cannot be ignored as it is the underlying principle for current electricity. A good grasp of this law and related topics like power, internal resistance, and Kirchhoff’s law can secure you four to eight marks in NEET. It is necessary to understand Ohm’s law to save time during the exam, avoid calculation errors, and fetch marks in this competitive exam.

Why was Ohm’s Law needed by scientists?

Electricity was unclear and uncertain before the discovery of Ohm’s Law by Georg Simon Ohm. The flow of electricity was recognized, but its nature was not properly defined. Before scientists could regulate the current in circuits and measure the characteristics, a rule connecting voltage, current, and resistance had to be discovered. Ohm’s law was essential to ensure scientists measured electricity, predicted the behavior of electricity in a circuit, and constructed reliable electrical appliances.

• Clear Relationship: It established the relationship between voltage, current, and resistance in an electrical circuit.
• Measurable Electricity: It ensured that scientists could analyze diverse materials under similar experimental conditions and accurately record measurements.
• Circuit Design: With Ohm’s Law, engineers could design effective electrical devices and machines with controlled electric currents.
• Decreased Guesswork: Ohm’s Law decreased guesswork by providing scientists with a reliable mathematical model for exploring electricity in circuits.

What is Ohm's Law?

A fundamental law of physics called Ohm’s law states that the current in a circuit is directly proportional to the potential difference across the ends of a conductor when the temperature remains constant.

V = IR

V (Voltage / Potential Difference): It is the electrical driving force. It is measured in volts (V).

I (Current): It is the rate of charge flow through the conductor. I is measured in amperes (A).

R (Resistance): It is the opposition to the flow of electric charge. It is measured in ohms (Ω).

Symbol	Term	Description
V	Voltage / Potential Difference	Electrical driving force. Unit: Volt (V)
I	Current	Rate of charge flow. Unit: Ampere (A)
R	Resistance	Opposition to charge flow. Unit: Ohm (Ω)

Devices Based on Ohm's Law:

Ohm’s law-based electric devices allow controlling current by means of its resistance, enabling the circuit to transform electrical energy into heat, light, and a limited amount of power.

• Electric heater: based on the principle of current passage through a conductor with resistance leading to the transformation of electricity into heat;
• Incandescent light bulb: based on the principle of electricity passage through a conductor with high resistance resulting in the appearance of visible radiation;
• Electric iron: based on the principle of resistance utilization for electricity transformation into heat with the help of limited current and voltage.
• Resistors in circuits: based on the principle of Ohm’s law and used to reduce voltage and control current.
• Fuse: based on the principle of resistance and power generation leading to the appearance of heat needed to cut off electric current;
• Rheostat or variable resistor: usually included in electric circuits for current control by means of resistance changes.

Typical Questions from Ohm’s Law

Question1:

Explanation: A 5 Ω resistor is connected to a 10 V power source, determine the current flowing through the resistor. According to Ohm’s Law, the mathematical equation used in determining current is given by I=V/R; therefore, calculating the current flowing through the resistor gives I=10/5=2A . Hence, there are 2 Amperes of current flowing through the resistor.

Question 2:

Explanation: Ohm’s Law states that when voltage is constant, current is inversely proportional to resistance, which means I∝1/R. Hence, if resistance increases from R to 2R, current decreases from I to I/2. As a result, when the resistance is doubled, the current halves while the voltage remains the same.

Question 3: 

Explanation: Voltage is plotted on the y-axis and the current is plotted on the x-axis in a V –I graph. A straight line passing through the origin is observed due to the direct proportionality of voltage and current. Ohm’s law explains this relationship by stating resistance equals voltage divided by current. From the graph, the slope is calculated as rise over run. Therefore, resistance can be described as the slope of the V –I graph.

Question 4: 

Explanation: As there is only one path for the current when the resistors are connected in series, the same amount of current flows through all of the resistors. The total resistance, or the equivalent resistance in the case of a series connection, is given as = R 1 +R 2 +R 3. Thus, the equivalent resistance increases, and the correct option is "Sum of resistances".

Question 5: 

Explanation: The rate at which electrical energy is converted into heat is known as power, which represents the energy consumption of the element. The power consumed by a resistor can be expressed in three equivalent forms using Ohm’s law: P = VI, P = I²R, and P = V²/R. These expressions can be derived from the basic relation V = IR. Therefore, the correct answer is “all of these,” since all three expressions are equivalent.

Question 6: 

Explanation: In metallic conductors, increased temperature leads to higher resistance due to the atoms vibrating intensively, thus impeding the movement of free electrons. The graph shows that as the temperature rises, the resistance also increases linearly with temperature, which implies a positive temperature coefficient. The correct answer is therefore “Increase.”

Question 7: 

Explanation: According to Ohm’s Law, Voltage and Current are directly proportional to each other, so their graph is a straight line. Copper, Nichrome, and metals have a linear V-I graph. But the diode has a nonlinear V-I graph, which allows the current to flow through it only in forward bias. Hence, option C is correct because a diode does not obey Ohm’s Law.

Question 8: 

Explanation: In a parallel circuit, current divides inversely with resistance, but the voltage across each resistor remains constant. Using the equivalent resistance formula R = (R1 × R2) / (R1 + R2), the equivalent resistance is calculated as R = (2 × 4) / (2 + 4) = 8 / 6 = 1.33 ohm.

Current division is also shown in the diagram: more current (6 A) flows through the lower resistance (2 ohm) than through the higher resistance (4 ohm, 3 A). Therefore, 1.33 ohm is the correct answer.

Question 9: 

Explanation: In a parallel circuit, current divides inversely with resistance, but the voltage across each resistor remains constant. Using the equivalent resistance formula R = (R1 × R2) / (R1 + R2), the equivalent resistance is calculated as:

R = (2 × 4) / (2 + 4) = 8 / 6 = 1.33 Ω.

Current division is also shown in the diagram: more current (6 A) flows through the lower resistance (2 Ω) than through the higher resistance (4 Ω, 3 A). Therefore, 1.33 Ω is the correct answer.

Question 10: 

Explanation: The drift velocity of the charge carriers in a conductor is related to the current in the conductor. Current increases with an increase in the drift velocity of the charge carriers. This can be seen in the equation I = nqAvd, where n is the number of charge carriers per volume, q is the charge of the particle, A is the area, and vd is the drift velocity. Current is generated by the movement of electrons in an electric field, as seen in the diagram. Therefore, drift velocity is the correct answer.

Also Watch: Most Repeated NEET IIT-JEE Physics Formula | Ohm’s Law Explained for Exams

Conclusion

Mastering Ohm’s Law is essential for tackling both direct and complex circuit problems in NEET Physics. By thoroughly understanding its core formula, graphical interpretations, non-ohmic exceptions, and resistor combinations, you build a strong foundation to solve numericals accurately, avoid common pitfalls, and confidently maximize your exam score.