 # Current Electricity

## Electric current is the rate of flow of electric charge per unit time. Conductors are the materials having large number of free electrons, due to which they develop strong electric currents, when an electric field is applied. In solid conductors, large numbers of free electrons are responsible for electric current. In liquid conductors, the positively and negatively charged ions are responsible for electric current. Conventional current is the current in which the direction of flow of positive charge gives the direction of electric current. Practically, the direction of flow of electrons gives the direction of electronic current. The direction of electrons flow is opposite to that of conventional current. Drift velocity is the velocity attained by the free electrons in the presence of an electric field. Drift velocity is defined as the average velocity with which the free electrons get drifted towards the positive end of the conductor under the influence of applied external electric field. Mobility is defined as the magnitude of the drift velocity per unit electric field  and the current flowing per unit area is called current density. Ohm’s law states that the current (I) flowing through a conductor is directly proportional to the potential difference (V) across the ends of the conductor, provided physical conditions of the conductor such as temperature, mechanical strain etc. are kept constant. The graph between potential difference and current through a conductor, is a straight line. Non-ohmic conductors are the substances that do not obey Ohm’s law. Substances classified as conductors, insulators and semi-conductors on the basis of resistance offered to the flow of current. The resistance of the conductor depends on the length and area of the conductor. The resistance is defined as the resistivity of the material for the unit length and unit area of conductor. Resistivity is temperature dependent and is different for different materials. The rate at which electric work is done by the source of e.m.f in maintaining the current in an electric circuit is known as Electric power. The total electric work done or energy supplied by the source of e.m.f in maintaining the current in an electric circuit for a given time is the electric energy consumed in the circuit. Resistances and cells are connected in either series or in parallel or in combination of both in a circuit. For solving complex circuits, Kirchhoff’s junction and loop rules are very useful. Wheat stone bridge is an important application of Kirchhoff’s rules. For determination of unknown resistance, Wheatstone bridge and its balance conditions are used. Meter bridge or slide wire bridge is a practical form of Wheatstone bridge. Potential (voltage) is measured by an instrument known as Potentiometer.The measuring method involves a condition of no current flow. It is also used to measure internal resistance of a cell and compare emf’s of two sources.  Electric current is the rate of flow of electric charge per unit time. Conductors are the materials having large number of free electrons, due to which they develop strong electric currents, when an electric field is applied. In solid conductors, large numbers of free electrons are responsible for electric current. In liquid conductors, the positively and negatively charged ions are responsible for electric current. Conventional current is the current in which the direction of flow of positive charge gives the direction of electric current. Practically, the direction of flow of electrons gives the direction of electronic current. The direction of electrons flow is opposite to that of conventional current. Drift velocity is the velocity attained by the free electrons in the presence of an electric field. Drift velocity is defined as the average velocity with which the free electrons get drifted towards the positive end of the conductor under the influence of applied external electric field. Mobility is defined as the magnitude of the drift velocity per unit electric field  and the current flowing per unit area is called current density. Ohm’s law states that the current (I) flowing through a conductor is directly proportional to the potential difference (V) across the ends of the conductor, provided physical conditions of the conductor such as temperature, mechanical strain etc. are kept constant. The graph between potential difference and current through a conductor, is a straight line. Non-ohmic conductors are the substances that do not obey Ohm’s law. Substances classified as conductors, insulators and semi-conductors on the basis of resistance offered to the flow of current. The resistance of the conductor depends on the length and area of the conductor. The resistance is defined as the resistivity of the material for the unit length and unit area of conductor. Resistivity is temperature dependent and is different for different materials. The rate at which electric work is done by the source of e.m.f in maintaining the current in an electric circuit is known as Electric power. The total electric work done or energy supplied by the source of e.m.f in maintaining the current in an electric circuit for a given time is the electric energy consumed in the circuit. Resistances and cells are connected in either series or in parallel or in combination of both in a circuit. For solving complex circuits, Kirchhoff’s junction and loop rules are very useful. Wheat stone bridge is an important application of Kirchhoff’s rules. For determination of unknown resistance, Wheatstone bridge and its balance conditions are used. Meter bridge or slide wire bridge is a practical form of Wheatstone bridge. Potential (voltage) is measured by an instrument known as Potentiometer.The measuring method involves a condition of no current flow. It is also used to measure internal resistance of a cell and compare emf’s of two sources.

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