Option 1 states that an electric motor converts electrical energy into mechanical energy. This statement is correct. Electric motors use the interaction between an electric current and a magnetic field to produce mechanical motion.

Option 2 states that an electric generator works on the principle of electromagnetic induction. This statement is correct. Electric generators use the principle of electromagnetic induction to convert mechanical energy into electrical energy. When a coil of wire is rotated in a magnetic field, it creates an electric current.

Option 3 states that the magnetic field at the center of a long circular coil carrying current will be parallel straight lines. This statement is incorrect. The magnetic field at the center of a long circular coil carrying current is actually circular and concentric with the coil. It is not parallel straight lines.

Option 4 states that a wire with green insulation is usually the live wire of an electric supply. This statement is not correct. In most electrical systems, the live wire is usually color-coded with black, brown, or red insulation, while green insulation is typically used for the ground wire.

Overall, the correct answer is option 4, as it is the statement that is not correct.