What Are the Properties of Magnets? Magnets have three main properties – Magnets attract iron and materials that contain iron. – Magnets attract or repel other magnets. – One end of a magnet always points North when allowed to swing freely.
How do Magnetic Poles Interact Each end of a magnet is called a magnetic pole. – Magnetic poles that are alike repel each other – Magnetic poles that are unlike attract each other – The magnetic effect is strongest at the poles
Magnetic Force – the attraction or repulsion between magnetic poles. – Produced when magnetic poles come near each other and interact. – Any material that exerts a magnetic force is a magnet.
Magnetic Fields The area of magnetic force around a magnet is known as it’s magnetic field Magnetic field lines map out the invisible magnetic field around a magnet. – Spread out from one pole – Curve around the magnet – Return to the other pole
Magnetic Fields Lines form complete loops and never cross Always leave the North Pole and enter the South Pole The closer the lines are the stronger the field Strong Magnetic Field Weak Magnetic Field
Single Magnetic Field Although you cannot see a magnetic field, you can see its effects. – The magnetic forces of the magnet act on the iron filings and align them along the invisible magnetic field lines.
Combined Magnetic Field The magnetic field of two or more magnets overlaps – The effects of magnetic force on iron filings when the poles of two magnets are brought near each other. – The fields from unlike poles attract each other, forming a strong field between the magnets.
Combined Magnetic Field – The fields from two like poles repel each other
Compass A compass is a device that has a magnet on a needle that spins freely; it is used for navigation because it’s needle usually points north.
Earth’s Magnetic Field The motion of Earth’s iron outer core creates a magnetic field similar to a bar magnet’s magnetic field.
Electric Charge The interaction between electric charges is called electricity. An electric field is a region around a charged object where the object’s electric force is exerted on other charged objects. When electric charges are made to flow through a material, they produce an electric current. An electric motor is a device that uses an electric current to turn an axle. – An electric motor transforms electrical energy into mechanical energy.
Electromagnetic Force Electromagnetism – the relationship between electricity and magnetism. An electric current produces a magnetic field. When there is no current in the wire, the compass needles all point north When current is present, the compass needles align with the magnetic field produced by the current in the wire.
Magnetic Fields Produced by a Current The magnetic field produced by a current has strength and direction. The field can be turned on or off – By turning the electric current on or off The field can have its direction reversed – By reversing the direction of the current The field can have it’s strength changed – By increasing the amount of current or by making a loop or coil in the wire.
Solenoids and Electromagnets - use electric current and coiled wires to produce strong magnetic fields A coil of wire with a current is called a solenoid. – The two ends of a solenoid act like the poles of a magnet, but the north and south pole change when the direction of the current changes.
A solenoid with a ferromagnetic core is called an electromagnet Magnetic field of an electromagnet is MUCH stronger that the magnetic field of a solenoid
There are four ways to make an electromagnet stronger 1.Increase the current in the solenoid 2.Add more loops of wire to the solenoid 3.Wind the coils of the solenoid more closely together 4.Use a material that is more magnetic than iron. – Example: Alnicol