Magnets and Magnetic Fields

• Magnets have north and south poles, like poles repel, and unlike poles attract.
• Permanent magnets are always magnetic and have poles.
• Induced magnets are materials that are "magnetic" but don't have fixed poles; stroking them with a permanent magnet can temporarily magnetize them by aligning their domains.
• Iron, nickel, and cobalt can become temporary magnets.

Magnetic Fields

• Field lines point from north to south, and strength decreases with distance from the magnet.
• The direction of the field always points towards the south pole and away from the north pole at any point.
• Plotting compasses indicate the direction of the magnetic field at a specific point.
• Earth's magnetic core creates a large magnetic field, causing a freely suspended compass to align with its field lines and point North.
• Earth's magnetic north pole is located over northern Canada and is a magnetic south pole, while the geographic south pole is near the magnetic north pole.

Current and Magnetic Fields

• Current produces a magnetic field around a wire, with the direction dictated by the "right hand grip rule".
• Stronger current results in a stronger magnetic field; greater distance from the wire results in a weaker field.

Solenoids

• Solenoids have a magnetic field shape similar to a bar magnet.
• Coiling the wire enhances the magnetic effect, aligning the field to form a single strong field.
• Placing an iron core inside increases strength, as magnetic field lines pass through iron more easily than air.
• Factors affecting solenoid strength include current size, length, cross-sectional area, number of turns (coils), and using a soft iron core.

Motor Effect

• Two magnets interact, generating a magnetic force of attraction/repulsion.
• A magnet and a wire (with current) will also exert a force due to interaction of their magnetic fields.
• The magnetic field around a wire is circular, but between two magnets, it is straight.
• When the two fields interact, the wire is pushed away from the field between the poles.
• Fixed permanent magnets have field lines along the x-axis, a wire with current is along the y-axis, and the resulting force is along the z-axis.
• Fleming's Left Hand Rule determines the direction of force, current, and magnetic field, each at 90° to each other.
• Remember that current moves in the opposite direction to the electrons.
• Magnetic Flux Density (B) is measured in Tesla and is the number of flux lines per meter squared.
• F = BIl

Electric Motors

• Permanent magnets are in fixed positions, with a coil of current-carrying wire on an axis in between.
• Force on one side moves that side up, while force on the opposite side moves it down, causing rotation, which is verified by Fleming's Left Hand Rule.

Electromagnetic Induction

• Relative movement between a conductor and a magnetic field induces a potential difference across the conductor.
• A current flows if the conductor forms a complete circuit, producing its own magnetic field that opposes the change inducing it.
• Electric generators (dynamos) function similarly to motors, with a rotating coil of wire between two permanent magnets.
• A turbine spins, turning the coil of wire, causing it to cut through the magnetic field and experience a change in the magnetic field, creating a potential difference.
• If the coil is connected to a complete circuit, an alternating current (AC) will flow.
• A basic alternator produces AC current, while a split ring commutator reverses the current each half-rotation to produce direct current (DC), in a system called a dynamo.

Transformers

• AC in a primary coil creates a changing magnetic field, which cuts through the secondary coil and induces a current, also AC.
• If the primary current was DC, the magnetic field produced would be constant, inducing nothing in the secondary coil.
• More coils on the secondary coil result in a step-up transformer, increasing voltage, while fewer coils result in a step-down transformer, decreasing voltage.
• Power(primary) = Power(secondary)
• Vp Ip = Vs Is
• This works with current if the transformer is 100% efficient.

Dynamic Microphones

• Produce a current proportional to the sound signal.
• A fixed magnet is at the center, with a coil of wire around the magnet free to move.
• Pressure variations in sound waves cause the coil to move, inducing a current as it cuts the magnetic field.
• This current is sent to a loudspeaker.

Loudspeakers

• The setup mirrors that of dynamic microphones but works in reverse.
• Current flows into the coil, and the magnetic fields from the magnet and current interact, causing the coil to move.
• The cone moves, producing pressure variations and making sound.

Explore magnets, their poles, and interactions. Investigate permanent and induced magnets, along with materials like iron, nickel, and cobalt. Learn about magnetic fields, their direction, and Earth's magnetic core.