What type of core should be put inside a current-carrying solenoid to make an electromagnet ?

What is the shape of field lines inside a current-carrying solenoid? What does the pattern of field lines inside a current-carrying solenoid indicate?

List three ways in which the magnetic field strength of a current-carrying solenoid can be increased?

What is an electromagnet? Describe the construction and working of an electromagnet with the help of a labelled diagram.

Explain why, an electromagnet is called a temporary magnet.