Choose the incorrect option.
(c) A bar magnet, with the help of a bar magnet, is a permanent magnet.
(d) The magnetic field of a solenoid is constant.
(a) A bar magnet, with the help of a bar magnet, is a temporary magnet.
(b) A solenoid's magnetic field is not constant.
(c) A bar magnet, without the help of a bar magnet, is a permanent magnet.
(d) The magnetic field of a solenoid is variable.
