Magnetic Effects of Electric Current

For a current in a long straight solenoid N-pole and S-pole are created at the two ends. Among the following statements, the incorrect statement is

Commercial electric motors do not use

Choose the incorrect statement

The strength of magnetic field inside a long current carrying straight solenoid is

To convert an AC generator into DC generator

The most important safety method used for protecting home appliances from short circuiting or overloading is