Magnetic Fields

Magnets Magnets are polarized Magnets are polarized –It has two distinct and opposite ends North-seeking pole North-seeking pole South-seeking pole South-seeking pole –Every magnet will have both north and south poles

Like magnetic poles repel Like magnetic poles repel Opposite magnetic poles attract Opposite magnetic poles attract –North will repel north, but attract the south pole of a magnet –South will repel south, but attract the north pole of a magnet

Magnetic Fields Magnetic fields are vector quantities that exist in a region in space where a magnetic force occurs. Magnetic fields are vector quantities that exist in a region in space where a magnetic force occurs. The presence of a magnetic field can be seen using iron filings The presence of a magnetic field can be seen using iron filings These iron filings would make up a two- dimensional plot of the field These iron filings would make up a two- dimensional plot of the field –This makes visualizing the magnetic field lines possible

Magnetic field lines, like electric field lines are imaginary. Magnetic field lines, like electric field lines are imaginary. They are used to help us visualize a field They are used to help us visualize a field

Magnetic Flux The number of magnetic field lines passing through a surface is called the magnetic flux The number of magnetic field lines passing through a surface is called the magnetic flux The flux per unit area is proportional to the strength of the magnetic field The flux per unit area is proportional to the strength of the magnetic field The magnetic flux is most concentrated at the poles, thus this is where the magnetic field strength is the greatest The magnetic flux is most concentrated at the poles, thus this is where the magnetic field strength is the greatest

The direction of the magnetic field line is the direction in which the north pole of a compass points when it is placed in the magnetic field. The direction of the magnetic field line is the direction in which the north pole of a compass points when it is placed in the magnetic field. –So, field lines emerge from the magnet at its north pole and enter at its south pole

There are no isolated poles in the magnet so the field lines even travel through the magnet itself to go from the south pole to the north pole and form closed loops There are no isolated poles in the magnet so the field lines even travel through the magnet itself to go from the south pole to the north pole and form closed loops

Creating a Magnet You can create a magnet by having an electric current travel through a wire coil You can create a magnet by having an electric current travel through a wire coil The current carrying coil will repel the north end of a magnet on one side and attract on the other The current carrying coil will repel the north end of a magnet on one side and attract on the other –This means that that coil has a north and south pole and is itself a magnet This is called an electromagnet This is called an electromagnet You can increase the strength of the electromagnet by placing an iron rod or core within the coil of wire. You can increase the strength of the electromagnet by placing an iron rod or core within the coil of wire.

Magnetic field strength  B Magnetic field strength  B –This is also known as the flux density The weber, Wb, is a derived SI unit for measuring the number of lines of flux. The weber, Wb, is a derived SI unit for measuring the number of lines of flux. The tesla, T, is the derived SI unit of flux density or magnetic field strength The tesla, T, is the derived SI unit of flux density or magnetic field strength –One tesla is equal to one weber per square meter. Therefore, magnetic field strengths (B) are measured in units of teslas (T) Therefore, magnetic field strengths (B) are measured in units of teslas (T)