Ohm’s Law and Resistance

Ohm's Law and Resistance

In this article we will learn basic about Resistance and Ohm’s law. Resistance is a property of an element that offers opposition to the flow of current. The symbol of resistance is as shown in the below figure.

symbol of resistance
symbol of resistance

All elements of circuits have some opposition to the flow of current and that termed as resistance. Due to thermal conditions, the free electrons of atoms of the conductor vibrates. But this is not enough to flow the current.

When a voltage source applied across such a conductor an electric field created and electrons move in a direction opposite to that of the electric field and thus building current.

This was explained by ohm and ohm’s law defined as,

“Electric current is proportional to voltage and inversely proportional to resistance.”

According to ohm’s law,

    \[ I \propto {V} \]

    \[ V = IR \]

Where R is proportionality constant and known as resistance.

Graphical Representation of Ohm's Law
Graphical Representation of Ohm’s Law

Resistance is,

  • Proportional to length of the conductor
  • Inversionally proportional to the conductor
  • Dependent on temperature

    \[ R \propto \frac{L}{A} \]

    \[ R = \rho \frac{L}{A} \]

Where L is length of conductor and A is area of conductor.

Where ρ (rho) is proportionality and it’s called resistivity or specific resistance of the material. Resistivity refers to the nature of the material.

Resistance may also be thought of as a property of an element that converts electrical energy into heat energy. The power absorbed by a resistor denoted as P and formulate as below equations.

    \[ P = VI = (IR)I = I^2 R \]

If the current is a time-variant quantity ‘I’, the amount of energy converted into heat during time interval t2 to t1 can be written as,

    \[ P = \int_{t_1}^{t_2} I^2 R dt \]

When current is a constant quantity ‘I’ heat energy is written as

    \[ P = I^2 Rt \]

The unit of P is joule. All resistance produces heat while carrying current which is given by I2R.

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