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Electric current - The amount of charge flowing through one cross section of a conductor is called Electric current. Its SI Unit is Ampere (A)
POTENTIAL: The electric potential at a point is defined as the amount of work done per unit charge in bringing a positive test charge from infinity to that point. The S.I. unit of electric potential is volt.
The potential difference (p.d.) between two points is equal to the work done per unit charge in moving a positive test charge from one point to the other. It's S.I. unit is volt. It is a scalar quantity.
RESISTANCE:
The obstruction offered to the flow of current by the conductor (or wire) is called it's resistance.
The S.I. unit of resistance is Ohm.
OHM'S LAW:
According to Ohm's law, the current flowing in a conductor is directly proportional to the potential difference applied across it's ends provided that the physical conditions and the temperature of the conductor remain constant. V = IR.
The conductors which obey the Ohm's law are called the ohmic resistors or linear resistances. Examples are all metallic conductors (such as Silver, Aluminium, Copper, Iron etc.)
The conductors which do not obey the Ohm's law are known as the non-ohmic resistors
In a thick conductor, electrons get a larger area of cross section to flow as compared to a thin conductor, therefore a thick wire offers less resistance. The resistance of a conductor is inversely proportional to it's area of cross section (a), normal to the direction of flow of current i.e.,
Resistance of a wire is directly proportional to the length of the wire.
In a long conductor, the number of collisions of free electrons with the positive ions will be more as compared to a shorter one. Therefore, a longer conductor offers more resistance. Hence, the resistance of a conductor is directly proportional to the length of the wire.
With the increase in temperature of a conductor, the random motion of electrons increases. As a result, the number of collisions of electrons with the positive ions increase. Hence, the resistance of a conductor increases with an increase in it's temperature.
The three factors on which the resistance of wire depends are -
Dependence on length of the wire - the resistance of a wire is directly proportional to the length of the wire
Dependence on the thickness of the wire - the resistance of a wire is inversely proportional to it's area of cross section (a) normal to the direction of flow of current.
Specific resistance of a material is the resistance of a wire of that material of unit length and unit area of cross section.
The S.I is Ω-m
Dependence on the temperature of the wire - the resistance of conductor increases with an increase in it's temperature.
Standard resistors are made of magnanin, constantan etc. for which the specific resistance is high and the effect of change in temperature on their resistance is negligible
The material used for making fuse wire is an alloy of lead and tin because it's melting point is low and it's specific resistance is more than that of copper or aluminium so that the resistance of a short and thin fuse wire is more than that of the connecting wire. It permits current upto it's safe limit to pass through it, but an excessive current melts it so that it blows off and the circuit is broken.
e.m.f of a cell is defined as the energy spent (or the work done) per unit charge in taking a positive test charge around the complete circuit of the cell.
Terminal voltage - The terminal voltage of a cell is defined as the work done per unit charge in carrying a positive test charge around the circuit connected across the terminals of the cell.
Internal resistance - The resistance offered by the electrolyte inside the cell, to the flow of current, is known as the internal resistance of the cell.
The factors on which the internal resistance of a cell depends are -
The surface area of the electrodes - larger the surface area of electrodes, less is the internal resistance.
The distance between the electrodes - more the distance between the electrodes, greater is the internal resistance.
(i) The household unit of electricity is kWh
kWh is the electrical energy consumed by an electrical appliance of power 1 kilowatt when it is used for 1 hour.
(ii) The voltage of the electricity that is generally supplied to a house is 220 volt.
(iii) The electrical energy is consumed by various