Resistors in Series and in Parallel

There are two ways arranging resistors, series circuits and parallel circuits.


In a series circuit, the resistors are arranged in a chain, so the current has only one path to take and is the same through each resistor. The total resistance is equal to the sum of the resistances:


In a parallel circuit the resistors are arranged with their heads connected together, and their tails connected together.


The current breaks up and flow among each different branch through the resistors and re-combining when the branches meet again. The voltage through each parallel resistor is the same. The total resistance is reduced and is given by the relationship:


Ohm’s Law

The power source V, leads electric current I through the resistor R. Thus we can say that the three quantities obey the law of Ohm.

Ohm’s Law relates the voltage (V), the current (I) and resistance (R).


Ohm discovered that the current in a circuit is directly proportional to the voltage applied to the edges of a circuit and inversely proportional to the resistance of the circuit.

V = I x R

This relationship can be expressed in three ways:

I = V / R

R = V / I

V = I x R


V    = voltage (Volts)

I     = current (Ampere)

R    = resistance (Ohm)

The corresponding relationship between units is: Ampere = Volts / Ohm

Thus in a given circuit, the voltage and the current are proportional to each other. This implies that if we double the voltage across the circuit, the current will be doubled; the higher the voltage, the greater the current. However, if we double the resistance of the circuit, the current will reduced by half; the greater the resistance, the less the current.

So by applying the relation V = I x R, if we know any two of the three quantities, we can find the third.

According to Ohm’s law if it is applied potential difference of 1 Volt to the edges of a circuit having a resistance of 1 Ohm, will be generate a current of 1 Ampere.

Standard Electrical SI Units and Prefixes

Standard Electrical SI Units

In order that each of the SI units and quantities can be standardized across the globe, it is necessary to have exact definitions of each of them. The SI units are System International units that form the basis of the International System of Units.

Physical SI Units


Common Electrical Units

The standard SI units used in electrical or electronic circuits and systems are given in the following table. The table gives also a list of some of the standard electrical units of measure used as well as the electrical formulas and component values.


Metric Prefixes
In order to describe different values according to their size it is important to set up a range of metric prefixes for the values standard electrical units. By using multiples of the standard unit we can avoid having to write too many zero’s to define the position of the decimal point.



Try to convert

The conversion from one prefix to another it’s easy. The only thing you have to do is either multiply or divide by the difference between the two values.

Example: Convert 1MHz into kHz.

We know that: 1MHz  = 1,000,000Hz and 1kHz = 1,000Hz

So, 1MHz is one thousand times bigger than 1kHz.

To convert MHz into KHz we have to multiply MHz by one thousand, as 1MHz is equal to 1000 kHz.

Current, circuits and resistance

Different kind of electronic devices broadcast sounds, display images, takes measurements, record and “remembers” information, perform calculations and regulate other devices. Electronics is the science and technology of the motion of electrons in gas, vacuum, or in any semiconductor. A device is called electronic if it is comprised of parts where the movement of tiny particles (electrons) generate electricity directly controlled by electric or magnetic fields. In electronic devices a power forms to control another. For example, in a computer the changes that occur when you press the buttons regulate the data written on the hard disk. Electricity in this way allows quick and inexpensive implementation of complex functions. Everyone today is exposed to electronic and circuit devices, so it’s important to gain the basic knowledge of electronics, electricity and circuits. If you are interested to learn some basic electronics keep reading the following information guide.

DC & AC current

Electricity is the movement of electrical charges directed along an electrified conductor.
The amperage is time dependent. Thus, there are two kinds of electricity, direct current (DC) and alternating (AC).

DC is defined as the constant flow of electrons in the same direction, for example in a cable. DC can also be considered as the current, which varies the price and not the polarity over time. This feature separates DC from AC.
The alternating current is the electric current where both the intensity and the direction changing periodically. Unlike direct current, alternating current is transmitted easily and with low cost. Fewer losses arising during transportation which can be done with thinner wires. The alternating current is considered dominant over DC because of the possibility of converting the voltage to lower or higher prices.

Electronic Circuit

An electrical circuit is called a closed electrical circuit if electric current flows through it. Observe a battery, the lamp or any other electrical device. You will find that each such device has two edges those two poles. If you connect the cable ends of a battery with the ends of a light bulb, you will notice that the lamp illuminates. Inside the cable and the lamp electrons move in the direction from negative towards the positive terminal of the battery. In addition are moving into the battery in the direction of the positive to the negative pole. Namely electrons follow a closed path. In this case we say that we have a closed electrical circuit.

An open circuit is when we stop the flow of electrical current to the circuit. Try to disconnect the wire by one pole of the battery or from one end of the lamp. We observe that the lamp goes out. This is because between the free end of the wire and the battery pole or terminal of the lamp interposed air which is an insulator. The electrons cannot move within it consistently and their movement within the bulb the battery stops. Thus, the electrical circuit is called an open circuit.


From physics it is known that the property of a body to restrict the flow of electrical current through the electrical resistance is called. The resistance is denoted by the letter R (Resistance).
In order to understand the electrical resistance in depth you can check out the correlation between electrical and hydraulic systems.