Define Electric Current. Describe beriefly types of current electricity according to the frequency.

 Electric Current:  

It is the flow of electrons through any material conductor when a potential difference exists between the two ends of the conducting pathway.

The SI unit of electrical current is the ampere, defined as 1 coulomb/second. Current is a quantity, meaning it is the same number regardless of the direction of the flow, without a positive or negative number. However, in circuit analysis, the direction of current is relevant.

The conventional symbol for current is I.

Types of current electricity according to the frequency: 

On the basis of direction of folw of current.

1. Direct current.
2. Alternating current.

Direct Current: (DC):

In this type of electric current, direction is always same. The electric current generated from a cell or battery is DC. Due to the same direction of Direct Current, its frequency is ZERO. In DC Current one end is Positive (+) and the other end is Negative (-).

 

Alternative Current (AC)

Electrical current whose direction and value keeps changing is known as Alternating Current (AC). The value of AC current in one direction increases from ZERO to Maximum and fall down to ZERO and then in opposite direction it increases from ZERO to Maximum again and come back to ZERO. Due to this increase in both directions, the graph of AC looks like a Wave. This is called sine wave. In Alternate Current or AC, 50 such cycles or waves come in ONE Second. One side of AC is PHASE and the other side is NEUTRAL.

Alternating current is divided into three types..

1.      High frequency currents: frequency more than 1MHz e.g. SWD, MWD, UST

2.      Medium frequency: range of 100 to 4000 e.g. interferential currents

3.      Low frequency: range of 50 to 100 Hz e.g. IDC, Faradic, galvanic, sinusoidal, TENS

On the basis of voltage...

1. High voltage currents: greater than 100 volt
2.  Low voltage currents: less than100 Volt

Low frequency alternating current is again divided into four types for therapeutic purpose...

1. Faradic current 
2. Galvanic current 
3. Sinusoidal current 
4. Dynamic current