Magnetism and Electromagnetism

• Magnets produce magnetic fields
• Lines go from North to South in a magnetic field
• The closer the lines in a magnetic field, the stronger the magnetic field
• Induced Magnets only attract and are only magnetic when they are in a magnetic field
• Permanent Magnets produce their own magnetic field and can either attract or repel
• Compasses show the direction of magnetic fields
• A moving charge creates a magnetic field
• The Right Hand Rule can be used to show the magnetic field around a current carrying wire
• A solenoid is a coil of wire
• When a current flows through a solenoid, it produces a strong magnetic field inside the solenoid
• Electromagnets have lots of uses such as in cranes and within circuits
• The Motor Effect: A current in a magnetic field experiences a force
• The Size of a force acting on a conductor in a magnetic field can be found using the formula: Force = Magnetic Flux Density x Current x Length
• Fleming's Left Hand Rule: thumb = force, index finger = direction, middle finger = Current
• A current carrying wire rotates in a magnetic field. The magnetic field lines are perpendicular to the wire.
• Split Ring Commutators use brushes and momentum to switch the direction of the current in an DC motor
• Loudspeakers work because of the motor effect
• Variations in current in a loudspeaker cause the cone to vibrate and produce sound
• The Generator Effect is the induction of a potential difference in a wire when a current is induced in it
• The Potential Difference is reversed if you reverse the poles in a conductor
• Induced current opposes the change that made it
• Increase the speed of movement or increase the strength of the magnet to change the amount of induced Potential Difference
• To strengthen an electromagnet, add more turns to the coil, increase the current or add an iron core
• Alternators generate alternating current using a slip ring commutator and brushes.
• Dynamos generate direct current and use split-ring commutators to keep the current flowing in the same direction
• An oscilloscope can be used to see the generated Potential Difference
• Microphones generate current from sound waves
• Microphones are loudspeakers in reverse
• Transformers change the potential difference but only for alternating current
• Transformers have two coils of wire joined by an iron core
• Step-Up Transformers increase the potential difference and have more turns on the secondary coil
• Step-Down Transformers decrease the potential difference and have more turns on the primary coil
• Transformers are almost 100% efficient, meaning that the energy transferred is almost entirely transferred to the load