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Symbols used in electric circuit, A diagram which shows how different components in a circuit have been connected using conventional symbols for the components is called a circuit diagram., Electrical Potential, Electric potential is the work done in carrying a unit positive charge from infinity to a point., If W is the work done q is the charge, then electric potential V = W/q The SI unit of electric potential is Volts (V), Electric Potential Difference, The electric potential difference between two points is the work done in carrying a unit positive charge from one point to the other., The electric potential difference between points A and B, VAB = Work done to carry charge q from A to B / charge q The SI unit of electric potential difference is Volts (V), Electric Potential energy, Electric potential energy is the work which has to be done to bring charges to their respective locations against the electric field with the help of a source of energy. This work done is stored in the form of potential energy of the charges., Ohm’s Law, Under similar physical conditions, the current flowing through a wire is directly proportional to the difference in potential applied across its ends., I  V, V = I × R, where R is the resistance offered., Resistance, Resistance is the opposition to the flow of current., The SI unit of resistance is OHM (Ω), 1 ohm is the resistance offered by a wire carrying 1 A current when 1 V is applied across its ends., Factors Affecting Resistance, The resistance of a conducting wire depends on:, Nature of the material of the wire (Resistivity- Ω), Length of the wire (l), Cross-sectional area of the wire (A), R = Ω (l/A), Resistivity, The resistance offered by a wire of unit length and unit cross-sectional area is called resistivity., The SI unit of resistivity is ohm-meter (Ω − m)., Resistivity is also referred to as specific resistance., Reciprocal of resistivity is called conductivity., Conductivity, Ω = 1/ Ω Ω., SI unit of conductivity is ohm-1 m -1 or mho-m-1, Effect of Temperature, The resistivity of a conductor increases linearly with increase in temperature., The resistivity of an insulator increases with increase in temperature., The resistivity of a semiconductor decreases with increase in temperature. Resistivity of an alloy increases with increase in temperature., Semiconductors and Superconductors, Materials having resistivity between that of an insulator and a conductor are called semiconductors., Materials which lose their resistivity at low temperatures are called super conductors., Resistances in Series, If resistances R1, R2 and R3 are connected in series the equivalent resistance Rs = R1 + R2 + R3, Resistances in Parallel, If resistances R1, R2 and R3 are connected in parallel the equivalent resistance Rp is given by 1 =, Rp, (1/R1) + (1/R2) + (1/R3), Electrical Energy, Because of the existence of resistance to the flow of current work has to be done in order to maintain the flow of current., Since the potential difference V is the work done to carry unit positive charge from infinity to a point, the work done to carry a charge q is given by:, W= qV, But I = q/t, So W = ItV, Since V = I R, W = I2Rt = V2t/R, This work done is stored as energy. SI unit of electrical energy is Joule., Joule’s Law of Heating, When a current I flows through a resistor R heat is produced., H = I2Rt, this is Joule’s law of heating., Electric Power, The rate at which electric energy is consumed is called electric power., Power = work done/time., P = W/t = V × I = I2 R = V2R SI unit of electric power is Watt., Calculation of Power for House Hold Electricity, Kilowatt hour (kWh) is the commercial unit for electrical energy, 1 kWh = 3.6 × 106 J, No. of units of electricity consumed in a household = no. of kWh, Total cost of electricity = total units × cost per unit of electricity, Fuse Wire, The wire which melts, breaks the circuit and prevents the damage of various appliances in household connections is called a fuse wire, A fuse wire is made of an alloy of aluminium, copper, iron and lead, The thickness of the fuse wire increases the maximum safe current that can flow through it