Understanding the Question

The question asks to identify the fundamental law of electricity that describes the relationship between current and voltage in a closed circuit, specifically under the condition that physical conditions are kept constant. This relationship is stated as current being directly proportional to voltage.

Ohm's Law Explanation

Ohm's law is a key principle in electrical circuits. It establishes a relationship between voltage, current, and resistance. The law states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points, provided the temperature and other physical conditions remain unchanged.

Mathematically, Ohm's law is expressed as:

\[ V = I \times R \]

Where:

• \(V\) is the voltage across the conductor.
• \(I\) is the current flowing through the conductor.
• \(R\) is the resistance of the conductor.

From this equation, we can see that if resistance \(R\) is constant (which it is when physical conditions like temperature are constant), then \(I\) is directly proportional to \(V\). This perfectly matches the description given in the question.

Analyzing Other Options

Let's consider why the other options do not fit the description:

• Voltage law: This is a general term. Kirchhoff's Voltage Law (KVL) is a specific voltage law which states that the sum of all voltage drops around any closed loop in a circuit equals zero. This is different from the relationship described in the question.
• Current law: Similarly, this is a general term. Kirchhoff's Current Law (KCL) is a specific current law which states that the total current entering a circuit junction is equal to the total current leaving the junction. This deals with current division at a point, not the overall voltage-current proportionality in a circuit under constant physical conditions.
• Kirchhoff's law: Kirchhoff's laws (KCL and KVL) are fundamental laws used for analyzing circuits, especially complex ones. While related to voltage and current, they describe relationships within a circuit (sum of voltages in a loop, sum of currents at a junction) rather than the direct proportionality between voltage and current across a component or circuit under constant physical conditions as stated in the question.

Conclusion

The law that specifically states that in any closed circuit, current is directly proportional to voltage, provided physical conditions (like temperature) are kept constant, is Ohm's law. This makes Ohm's law the correct answer.