Electricity is the most commonly used form of energy. Electricity involves flow of electric current which happens due to continuous flow of electric charge. Electric current flows through a conductor when there is a potential difference between the ends of the conductor. Conventionally, the direction of electric current in a circuit is from positive terminal to the negative terminal of the battery. The actual flow of electrons, which constitute the electric current, is from negative terminal to positive terminal of the battery. An electric circuit is a closed conducting path for the flow of electric current. It consists of components like resistances, ammeters, voltmeters, switch and connecting wires connected between two terminal of a cell or a battery. Electric components are represented by symbols. A resistance in a simple circuit obeys Ohm’s law which states that at constant temperature, potential difference across the ends of a conductor is directly proportional to the current flowing through it. A graph plotted between V and I is a straight line. Resistance is the property of a conducting material to oppose the flow of current through it. Materials can be classified on the basis of their electrical resistance. A low resistance of a material implies an easy flow of electrical current through it and vice-versa. The resistance of a conductor depends on the length of a conductor, area of cross-section of the conductor, nature of the material of the conductor and the temperature of the conductor. Resistances in a circuit can be connected in series or parallel or combination of both. In series combination of resistances, the equivalent resistance is equal to the sum of individual resistances. In parallel combination of resistances, the reciprocal of equivalent resistance is equal to the sum of reciprocals of individual resistances. When electric current passes through a wire of high resistance such as nichrome, the wire becomes hot and produces heat. This is called the heating effect of electric current. The heating effect of current is the result of transformation of electric energy into heat and light energy. A number of heating appliances work on the basis of heating effect of current. When a current passes through an appliance, electrical energy is used up and converted into work. Electric power is the rate of doing work and it is rate at which electrical energy is consumed. The commercial unit of electric power is kilowatt-hour (kWh).
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