Electricity is all pervasive and we cannot imagine the comforts of modern life without electricity. All the electrical appliances get energy from electric current. Electric current flows through wires. A path through which electric current flows is called electric circuit. It is important to remember that current flows only through a closed circuit and never through an open circuit. A simple circuit contains a battery, a bulb, a switch and some wires. Circuit diagram is simple representation of an electric circuit. A circuit diagram is very helpful for mechanics and engineers.