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# Simple electrical circuit and its elements ## Simple electrical circuit A simple electrical circuit is one in which the current flows from the source to a load and reaches back the source to complete the path. The electrical circuit should consist of the following: * An energy source (cell) to...

# Simple electrical circuit and its elements ## Simple electrical circuit A simple electrical circuit is one in which the current flows from the source to a load and reaches back the source to complete the path. The electrical circuit should consist of the following: * An energy source (cell) to provide the voltage needed to force the current through the circuit. * Conductors through which the current can flow. * A load (resistor 'R') to control the amount of current and to convert the electrical energy to other forms. * A control device (switch 'S') to start or stop the flow of current. ## Electric current The flow of free electrons in a definite direction is called electric current. In other words, current is defined as the amount of charge 'Q' transferred over a time 't'. Actually the electrons flow is from the negative terminal of the battery to the lamp and reaches back to the positive terminal of the battery. However direction of current flow is taken conventionally from the +ve terminal of the battery to the lamp and back to the -ve terminal of the battery. Hence, we can conclude that conventional flow of current is opposite to the direction of the flow of electrons. The unit of current (I) is an ampere (A). An ammeter is used to measure the current in a circuit. It should be connected in series with the resistance (Load). Multiples of the ampere we use the following expressions: * 1 kilo-ampere = 1 kA = 1000 A = 1 x 103 A * 1 milli-ampere = 1 mA = 1/1000 A = 1 x 10-3 A * 1 micro-ampere " 1 μA" 1/1000000 A" 1 x 10-6 A ## Electromotive force (EMF) It is the electrical force, which is initially available in electrical source, cause to move the free electrons in a conductor Its unit is 'Volt' It is denoted by letter 'E' It cannot be measured by any meter. It can be only calculated by using the formula E = Potential Difference (P.D) + V. drop E = V + IR ## Potential Difference (PD) The difference of voltage and pressure across two points in a circuit is called a potential difference (p.d) and is measured in volts. In the circuit, when the switch is in open condition, the voltage across the terminals of the cell is called electromotive force (E) whereas when the switch is in the closed position, the voltage across the cell is called potential difference (p.d) which will be lesser in value than the electromotive force earlier measured. le EMF = voltage at the terminal of source of supply + voltage drop in the source of supply Emf = V1+IR ## Terminal voltage (p.d) It is the voltage available at the terminal of the source of supply. Its symbol is VT. Its unit is also the volt. V1 = EMF-IR Electrical voltage is measured with a voltmeter. The voltmeter connection is across or it is a parallel connection. For the decimal or decimal sub-multiples of the volt, we use the following expressions: * 1 kilo-volt = 1 KV = 1000 V = 1 x 103 V * 1 milli-volt = 1 mV = 1/1000 V = 1 x 10-3 V * 1 micro-volt " 1 μV" 1/100000