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Electric current basics

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Electric current basics

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 Electric Current

Current electricity or electric current consist of the movement of charges from one region of conductor to another. Therefore electric current is a movement of electron around the circuit.

 

electric current

electric current

Terms in  electric

  • Electric current
  • Resistance
  • Potential difference (p.d)
  • Cells
  • Electric Circuit
  • Resistivity
  • Conductivity
  • Resistor
  • Insulator
  • Ohm’s law

Electric current : it defined as  the movement of electric charges (electron) around the conductor or circuit. For example we enjoy electrical power in our home, which is made possible by movement of electric charges from power station. The electric current is measured in amperes. Electric current can be given mathematically as

electric current

electric current

Electric current=\quad \frac { quantities\quad of\quad charges\quad in\quad coulomb }{ time\quad taken }

That  is  \frac { Q }{ t }

Resistor: It anything that may not allow or slow or reduce the movement of electric current through a circuit or conductor.

Resistance: the process of not allowing or slowing or reducing the current passing through or around the circuit is known as resistance.

Potential difference: the potential difference between any two point in a circuit is defined as work done , when electric charge moves from one point to another. Note that charges are measured in coulomb while potential difference is measured in volts.

Cells: It can be defined as the source of power in electric circuit. The continuous flow of charges in a circuit is made possible by cells.

Electric circuit: It can be defined as the path provided for the flow of electric current. The electric circuit consist of , Cells, resistor, bulbs, and switch, which close of open the circuit. There are three type of circuit

  • Open circuit: this type of circuit is not complete as no electron can move around it.
  • Closed Circuit: this type of circuit is complete because current can flow through it.
  • Short circuit: here current is closed but no other thing connected to it except cells.

Resistivity:  The resistance of a resistor is directly proportional to the length and the inversely proportional to cross sectional area. Mathematically is given by

Resistance\quad R\quad =\frac { \rho L }{ A }

where l = length , A = cross sectional area

ρ =resistivity, therefore resistivity is given by

\rho \quad =\frac { RA }{ L }

Conductivity: it is the reciprocal of resistivity, that is

\sigma \quad =\frac { 1 }{ \rho }

where ơ =conductivity,  ρ = resistivity

Example: determine the length and conductivity of a wire with diameter of 2.omm constructed from an alloy of resistivity 22 x 10-8  Ωm, if its resistance is 0.42Ω

Solution

Resistance=\quad \frac { resistivity\quad \times \quad Length }{ Cross\quad sectional\quad Area } \quad

0.42=\frac { 22\quad \times \quad 10{ }^{ -8 }\quad \times \quad L }{ \frac { 22 }{ 7 } \quad \times \quad \left( 1\quad \times \quad 10{ }^{ -3 } \right) } \quad

L=\frac { 0.42\quad \times \quad 22\quad \times 10{ }^{ -6 } }{ 7\quad \times \quad 22\quad \times \quad 10{ }^{ -8 } } \quad =\quad 6.0m

Conductivity=\quad \frac { 1 }{ Resistivity } \quad

=  4.55 x 106(ΩM)-1 

   

Conductor: it is a substance that allows the flow of electric current through it.

Insulator: This is the substance that does not allow the flow of current through it at all.

The instrument used for measurement in  electric current

  • Ammeter : it is used to measurement of electric current
  • Galvanometer: It is an instrument used in measuring small electric current
  • Voltmeter; It used to measure voltage or potential difference in circuit.

OHM’S LAW

It state that a current passing through a metallic conductor (wire) at a constant temperature , is directly proportional to potential difference (p.d) applied between the two terminals.  This was found by a German, George Simon ohm in 1826, by experiment that  for a good conductor , there is relationship between the current flowing through it and the potential difference across it.

The mathematical expression of Ohm’s law is give by

V =IR      where V = potential difference,  I = current, and R = resistance

Limitations of Ohm’s Law

Ohm’s law hold for metallic conductor , and certain other , but the resistance of some conductor will change if they are placed under tension or bent into a loop. Also Ohm’s law is not applied to conductor such as radio valve, transistor and sem-conductor

How resistance and cells are connected in circuit: Cells or resistance can be connected in either Series or In parallel

 

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