Chapter 12

Electricity

Electric current

The flow of electric charge is known as Electric Current. It is expressed in terms of the rate of flow of charges.

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The SI unit of electric current is Ampere (A).
The direction of electric current is the same as the direction of positive charges and opposite to the direction of flow of negative charges.

Potential Difference

  • Work done per unit charge when taking charge from one point to another is known as the Potential Difference.
  • The unit of potential difference is volt (V).
  • 1V is defined as the potential difference between two points if 1 Joule of work is done to move 1-coulomb charge from one point to another.

Potential difference (V) between two points = Work done (W)/Charge (Q) V = W/Q

Electric Circuit Diagram
A circuit diagram is a simplified representation of the components of an electrical circuit using either the images of the distinct parts or standard symbols.
An electric circuit is a path through which electric current flows. An electric circuit can also be a closed path, thereby making it a loop. The flow of electric current is possible only when it is a closed circuit. An electric circuit can also be open circuit in which flow of electron is cut because of electric circuit is broken.

Ohms law

The potential difference between the two points is directly proportional to the current, provided the temperature is constant.
V l
V = lR

R is a constant known as Resistance. The SI unit of resistance is the ohm (Ω)
Factors on which resistance of a conductor depends-

  • It is directly proportional to the length of the conductor.
  • Inversely proportional to the area of cross-section.
  • Directly proportional to the temperature.
  • Depends on the nature of the material.

Resistivity
Resistivity is the property of the material. The SI unit of resistivity is ohm-metre.

  • The resistivity of metals varies from 10-8 to 10-6.
  • The resistivity of insulators varies from 1012 to 1017
  • Copper and aluminum are used in electrical transmission due to their low resistivity.
  • Resistance = Resistivity * Length of Conductor/Cross-Sectional Area