RESISTANCE

Electrical Circuit elements:

Concept of ENERGY FLOW, with the help of this energy flow we will try to understand the property and behavior of electrical circuit elements.

When energy flows from source to load, not 100% energy transferred to the load some energy get lost during this process in the form of heat, many things happens to the energy like transformed, unavailable and Stored.

1) Transformed: Energy transformed from electrical to mechanical, electrical to magnetic and electrical to heat energy.

2) Unavailable: Some energy will get lost, it means during the process of energy flow it will become unavailable to the load, some amount of energy will dissipate as heat.

3) Stored: During energy flow energy can be stored in two forms either in kinetic form or potential form, Later can be recovered and send either to load or back to the source.

So the energy lost in the component is resistor(R), energy get stored in the kinetic form, component call as a inductor (L) and in capacitor(C) energy is stored in the form of potential energy.

As we all aware any electrical circuit mainly consists of there elements viz resistor, inductor and capacitor. Property of these elements are resistance, inductance and capacitance respectively.

We will see all the elements one by one to know them in more detail.

1) RESISTOR: Resistor is not a dynamic component, it doesn't have history, memory and the past state.

It is the algebraic component, whatever is given to the input same will come as output.

✓ Property of Resistor:

• Dissipative

• Lossy

✓ Characteristics of Resistor: Generally we characterize the component in IV curve.

Fig.1

Fig.2

When resistor line aligned with the current(I) axis then slop will be zero and R will be infinite, which means it will represent short circuit at y axis.When resistor line aligned with the voltage(V) axis then slop will be zero and R will be infinite, which means it will represent open circuit at x axis. For this refer fig.1.

With the reference of fig.2 

current (I)= Voltage (V)/Resistance (R) --------(1)

Or V=IR  -------- Equation(2)

This is known as ohm's law.

POWER DISSIPATION IN RESISTOR

P=VI

Where,

V is the voltage across the resistance.

I is the current through the resistance.

According to equation (2)

P=(V*I)*I

P=I²R

According to equation (1)

P=V*(V/R)

P=V²/R

Resistance:

A material has property to oppose the flow of electrons through a given material, it is know as resistance of material. Different material has different resistivity like Aluminium, copper and gold has value of 2.82*10^-8 ohm-m, 1.72*10^-8 ohm-m and 2.44*10^-8 ohm-m respectively.

Thus resistance restricts the flow of electrons in the circuit.

* What is the flow of electrons?

Flow of electrons is current, and current is nothing but the flow of electrons in the material/conduct.

As per the ohms law:

R=V/I

Where 

R is resistance of the circuit,which is considered as 1 ohm.

V is voltage of the circuit, which is considered as 1 volt.

I is current of the circuit, which is considered as 1 Ampere.

Note: When electric current flow through the conductor it will generate heat due to collision of electrons within atom.

HOW TO FIND THE VALUE OF RESISTOR?

Fig.3

Fig.4

Now we will see how to find the resistor value?

Consider the above figure of resistor

Y   B  R

4   6   2

This is the resistor value = 46*10² ohms

Third value is the multiplier.

Note: keep in mind the last color code of the resistor shows the tolerance, which means variation of resistance with temperature.