Current as Flow of Charges - Advanced

All of us must have experienced that light in a room, light immediately after the switch is turned on.

Electric current is a flow of charges flowing through a conductor.

Let’s understand rate of the flow of charges.

Charge carriers in the wires of electric circuits are electrons. These electrons are simply supplied by the atoms of material the wire is made of within the metal wire.

If a charge Q flows through a cross-section of a conductor in time t, then-current I will be as:

The SI unit of charge is coulomb. It is the quantity of electricity carried in 1 second by a current of 1 ampere.  

A current of 1 ampere is 1 coulomb of charge going past a given point per second:

The relation between ampere and milliampere as follows:

We can tell the relation between milliampere and microampere as follows :

The particles that carry charge through wires in a circuit are mobile electrons.

We can not see the direction of flow of mobile electrons in the conductors.

When we switched on an electric bulb, it glows.

We can feel the direction of flow of current will be from the direction of a switch to the bulb.

Let’s understand the direction of flow of current.

Conventional direction of electric current is taken as opposite to the direction of flow of electrons.

Flow of electrons is in the opposite direction of the electric current.

We have encountered wires of different thickness, for bulbs connection, we use thin wires and thick wires for refrigerators.

Refrigerator needs more current than a bulb.

For the proper operation of electrical appliances, we should know the quantity of current required by the appliances.

Let’s understand ammeter.

Ammeter is an instrument for measuring either DC or AC electric current, in amperes. 

The main principle of ammeter is that it must have very low resistance and also inductive reactance.

Ammeter has very low impedance because it must have a very low amount of voltage drop across it.

Ammeter must be connected in series connection because the current is same in the series circuit.

Depending on the constructing principle, there are many types of ammeter.

Let’s understand types of ammeter.

Mainly four types of ammeter, permanent magnet moving coil ammeter, moving iron ammeter, electrodynamometer type ammeter, and rectifier type ammeter.

Depending on the types of measurement there are mainly direct current ammeter and alternating current ammeter.

We know that wires are made of solid materials and current flow through a wire.

Let’s understand the nature of flow of electrons in wires.

In conducting materials only a small fraction of all the electrons is free to move and carry current. The majority are too strongly bound to the respective nuclei.

The conduction electrons in a metal are non-localized. In conventional metals, each atom contributes a single such electron.

It is possible to neglect the mutual interaction of the conduction electrons since this interaction is largely shielded out by the stationary atoms.

The conduction electrons can, therefore, be treated as an ideal gas.

However, the concentration of such electrons in a metal far exceeds the concentration of particles in conventional gas. 

Revision

Electric current is a flow of charges flowing through a conductor.

The conventional direction of electric current is opposite to the direction of flow of electrons.

If a charge Q flows through a cross-section of a conductor in time t, then-current I will be as:  

Conventional direction of electric current is taken as opposite to the direction of flow of electrons.

Ammeter is an instrument for measuring either DC or AC electric current, in amperes. 

Ammeter must be connected in series connection.

The End