Magnetism

• The poles of a magnet are the places where the magnetic forces are strongest
• When two magnets are brought close together, they exert a force on each other
• Two like poles repel each other
• Two unlike poles attract each other
• Attraction and repulsion between two magnetic poles are examples of non-contact force
• A permanent magnet produces its own magnetic field
• An induced magnet is a material that becomes a magnet when it is placed in a magnetic field
• Induced magnetism always causes a force of attraction
• When removed from the magnetic field, an induced magnet loses most/all of its magnetism quickly
• A permanent magnet is a material that produces its own magnetic field regardless of circumstances. An induced magnet is a material that is magnetic only when it is placed in a magnetic field.
• The region around a magnet where a force acts on another magnet or on a magnetic material (iron, steel, cobalt and nickel) is called the magnetic field
• The force between a magnet and a magnetic material is always one of attraction
• The strength of the magnetic field depends on the distance from the magnet. The field is strongest at the poles of the magnet
• The direction of the magnetic field at any point is given by the direction of the force that would act on another north pole placed at that point
• The direction of a magnetic field line is from the north (seeking) pole of a magnet to the south (seeking) pole of the magnet
• A magnetic compass contains a small bar magnet
• The Earth has a magnetic field
• The compass needle points in the direction of the Earth’s magnetic field
• explain how the behaviour of a magnetic compass is related to evidence that the core of the Earth must be

  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 convection currents. in the Earth's core, which is made from iron and nickel.
• When a current flows through a conducting wire a magnetic field is produced around the wire. The strength of the magnetic field depends on the current through the wire and the distance from the wire. Shaping a wire to form a solenoid increases the strength of the magnetic field created by a current through the wire. The magnetic field inside a solenoid is strong and uniform. The magnetic field around a solenoid has a similar shape to that of a bar magnet. Adding an iron core increases the strength of the magnetic field of a solenoid.An electromagnet is a solenoid with an
• describe how the magnetic effect of a current can be demonstrated

  Plotting compasses on a piece of paper with a wire running through it will demonstrate this rule
• explain how a solenoid arrangement can increase the magnetic effect of the current.

  The small magnetic fields caused by the current in each turn of the coil add together to make a stronger overall magnetic field.
• When a conductor carrying a current is placed in a magnetic field the magnet producing the field and the conductor exert a force on each other. This is called the motor effect.
• factors that affect the size of the force on the conductor

  Current,magnetic flux density and length
• A coil of wire carrying a current in a magnetic field tends to rotate. This is the basis of an electric motor
• F=BIL

  force, F, in newtons, N magnetic flux density, B, in tesla, T current, I, in amperes, A (amp is acceptable for ampere) length, l, in metres, m
• When a current is passed through the coil, the coil spins because the force on the left hand side acts upwards & the force on the right hand side acts downward.
• Factors that affect the size of a conductor are

  Current: The larger the current, the larger the force. Length: The longer the length of the conductor, the larger the force. Magnetic Flux Density: The higher the density, the more magnetic field lines and the larger the force on the conductor.
• All magnets have two poles: north (or north seeking) and south (or south seeking)
• All magnets produce a magnetic field, a region where other magnets or magnetic materials (e.g. iron, steel, nickel, and cobalt) experience a non-contact force
• Magnetic field lines always go from north to south and show the direction and strength of the magnetic field
• The closer together the magnetic field lines are, the stronger the magnetic field and the stronger the force acting on a north pole placed in that point in the field
• The magnetic field is strongest at the poles of a magnet, where the magnetic forces are also strongest
• The force between a magnet and a magnetic material is always attractive, regardless of the pole
• Inside a compass is a tiny bar magnet, and the north pole of this magnet is attracted to the south pole of any other magnet it is near, pointing the compass in the direction of the magnetic field
• You can move a compass around a magnet and trace its position on paper to visualize the magnetic field
• There are two types of magnets: permanent magnets and induced magnets
• If two poles of a magnet are put near each other, they will exert a force on each other, which can be attractive or repulsive
• Compasses always point north when not near a magnet because the Earth generates its own magnetic field
• Permanent magnets produce their own magnetic field, while induced magnets are magnetic materials that turn into a magnet when put into a magnetic field