## 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

where:

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.