Magnetic fields
A Area surrounding a magnet that can exert a force on magnetic materials. is the region around a magnet where a force acts on another magnet or on a magnetic material.
Detecting magnetic fields
A magnetic field is invisible, but it can be detected using a magnetic compass. A compass contains a small bar magnet on a pivot so that it can rotate. The compass needle points in the direction of the Earth's magnetic field, or the magnetic field of a magnet.
Magnetic fields can be mapped out using small Small magnetic compass used to detect magnetic fields.:
- place the plotting compass near the magnet on a piece of paper
- mark the direction the compass needle points
- move the plotting compass to many different positions in the magnetic field, marking the needle direction each time
- join the points to show the field lines
The needle of a plotting compass points to the south pole of the magnet.
The Earth's magnetic field
The behaviour of a compass shows that the Earth has a magnetic field which means that the core of the Earth must be magnetic. Scientists believe that this field is produced by The motion of a liquid or gas caused by heating some part of that liquid or gas. in the Earth's core, which is made from iron and nickel. When a plotting compass is placed in the Earth's magnetic field, the north pole of the compass will line up with the Earth's magnetic field lines and point to magnetic south.
Drawing a magnetic field
The diagram shows the magnetic field around a bar magnet.
The diagram shows these key features:
- the An imaginary line which indicates the direction of force caused by a magnet. An arrow on the line shows the force direction on a magnetic north pole, so points from north to south. never cross each other
- the closer the lines, the stronger the magnetic field
- the lines have arrowheads to show the direction of the force exerted by a magnetic north pole
- the arrowheads point from the north pole of the magnet to its south pole