Read the text and choose the correct answer to the questions that
follow.
Electromagnet
An electromagnet is a type of magnet
in which the magnetic field is produced by the flow of electric current. The
magnetic field disappears when the current is turned off. Electromagnets are
widely used as components of other electrical devices, such as motors,
generators, relays, loudspeakers, hard disks, MRI machines, scientific instruments,
and magnetic separation equipment, as well as being employed as industrial
lifting electromagnets for picking up and moving heavy iron objects like scrap iron.
An electric current flowing in a
wire creates a magnetic field around the wire.
To concentrate the magnetic field,
in an electromagnet the wire is wound into a coil with many turns of wire lying
side by side. The magnetic field of all the turns of wire passes through the
center of the coil, creating a strong magnetic field there. A coil
forming the shape of a straight tube
(a helix) is called a solenoid; a solenoid that is bent into a donut shape so
that the ends meet is called a toroid. Much stronger magnetic inside the coil.
The ferromagnetic core increases the
magnetic field to thousands of times the strength of the field of the coil
alone, due to the high magnetic permeability μ of the ferromagnetic material.
This is called a ferromagnetic-core or iron-core electromagnet.
The direction of the magnetic field
through a coil of wire can be found from a form of the right-hand rule. If the
fingers of the right hand are curled around the coil in the direction of
current flow (conventional current, flow of positive charge) through the windings,
the thumb points in the direction of the field inside the coil. The side of the
magnet that the field lines emerge from is defined to be the north pole.
1) What electrical devices
contain electromagnets?