Current Electricity

Notes

1. Current Electricity

Current electricity is a branch of Physics. It deals with charges in motion.

Electricity

Electricity is a form of energy which is used to design electrical devices and make our life comfortable.

2. Electric Current

The flow of charges through the cross-sectional area of a conductor is called electric current.

The flowing charges through the cross-sectional area of a conductor constitute electric current.

The time rate of flow of charge is called electric current.

Expression for Electric Current

If Q is the amount of charge flowing through a cross-sectional area in time t, then:

I = Q/t

According to the definition:

Electric Current = Flow of Charge / Time

If:

Q = ne

then:

I = ne/t

Unit of Electric Current

• SI Unit: Ampere (A)
• CGS Unit: Statampere

Definition of One Ampere

The current is said to be one ampere if a charge of one coulomb flows through a conductor in one second.

1 A = 1 C/s

3. Current Carriers

A movable charge is called a current carrier.

Current Carriers in Different Substances

1. Solid
   • Conductor: Electrons or positive charges.
   • Insulator: No current carrier.
   • Semiconductor: Electrons or holes.
2. Liquid: Positive and negative ions act as current carriers.
3. Gas: Positive charges or electrons act as current carriers.

4. Source of Current

Any device which provides current is called a source of current.

Examples: Cell, battery, generator and solar panel.

5. Nature of Current

Electric current is a scalar quantity because it does not obey the laws of vector addition.

• Electric Current (I): Scalar quantity
• Current Density (J): Vector quantity

6. Direction of Current

The direction of current is:

1. In the direction of positive charge.
2. Opposite to the flow of electrons.
3. From higher potential to lower potential.
4. From cathode to anode in an external circuit.
5. From anode to cathode in an internal circuit.

7. Types of Current

Electric current is mainly of two types:

1. Direct Current (D.C.)
2. Alternating Current (A.C.)

7.1 Direct Current (D.C.)

The current whose direction remains fixed is called direct current.

Direct current is of two types:

1. Steady direct current
2. Variable direct current

Steady Direct Current