Question

Drawbacks of ohms law

Answer 1

The limitations of Ohms law are explained as follows: This law cannot be applied to unilateral networks. A unilateral network has unilateral elements like diode, transistors, etc., which do not have same voltage current relation for both directions of current. Ohms law is also not applicable for non – linear elements

Answer 2

The statement of Ohms law says that

This current (I) is directly proportional to the voltage (V) applied, provided temperature and all other factors remain constant. Mathematically, Where, R is constant of proportionality. This equation presents the statement of Ohm law. Here, we measure current in Ampere (or amps), voltage in unit of volt. The constant of proportionality R is the property of the conductor, we know it as resistance and measure it in ohm (Ω). Theoretically, the resistance has no dependence on the voltage applied, or on the flow of current. The value of R changes only if the conditions (like temperature, diameter and length etc.) of the resistor are changed by any means.

History of Ohm's Law In the month of May 1827, George Simon Ohm published a book "Die Galvanische Kette, Mathematisch Bearbeitet". "Die Galvanische Kette, Mathematisch Bearbeitet" means "The Galvanic Circuit Investigated Mathematically". He presented the relationship between voltage (V), current (I), and resistance (Ω) based on his experimental data, in this book. George Simon Ohm had defined the fundamental interrelationship between current, voltage and resistance of a circuit which was later named Ohms law. Because of this law and his excellence in the field of science and academics, he got the Copley Medal award in 1841. In 1872 the unit of electrical resistance was named 'OHM" in his honor. Ohm's Law Physics We an understand the physics behind Ohms law well if we examine it from molecular level of a material. A conductor contains free electrons. These free electrons randomly move in the conductor. When, we apply a voltage, across the conductor, the free electrons keep being accelerated towards higher potential end due to electrostatic force of the applied voltage. This means they acquire some kinetic energy as they move towards the + Ve end of the conductor. However, before they get very far they collide with an atom or ion, lose some of their kinetic energy and may bounce back. Again due to presence of static electric field the free electrons again accelerate. This keeps happening. That means, even after application of external electric field, there will be still random motion in the free electrons of the conductor. But each free electron drift towards +Ve end with its inherent random motion. As a result the free electrons tend to "drift" towards the + Ve end, bouncing around from atom to atom on the way. This is how materials resist current. If we apply more voltage across the conductor, the more free electrons will move with more acceleration which causes more drift velocity of the electrons. The drift velocity of the electrons is proportional to the applied static electric field. Hence the current (I) we get is also proportional to the applied voltage (V).