Section 6 - Electric And Magnetic Fields Flashcards
What is an electric field?
The region around an electrically charged object where if a second electrically charged object enters it, a force would be exerted on both objects.
which direction do electric field lines go?
Positive to negative
Which direction do magnetic field lines go?
North to south
State the three main magnetic elements
Iron
Nickel
Cobalt
How is an induced magnet created?
By putting a magnetic material inside a magnetic field
The right hand thumb rule
Thumb = current Fingers = magnetic field
What happens when a current flows through a long, straight conductor?
A magnetic field is created
What happens when a current-carrying conductor is put between two magnetic poles?
The two magnetic fields interact, causing a force on the wire.
Fleming’s left hand rule
Thumb = motion
Index finger = Field
Middle finger = Current
How do electric motors work?
A coil of wire is placed between two magnetic fields and a current is passed through it. Following the right hand thumb rule, the forces acting on the wire act in opposite directions causing the wire to spin. A split ring commutator swaps the contacts every half turn to keep the coil spinning in the same direction.
What is magnetic flux density measured in?
Tesla
What does a step up transformer do?
Increase the potential difference
What does a step down transformer do?
Decrease the potential difference
What kind of current does a dynamo create?
d.c
What kind of current does an alternator generate?
a.c
How does a dynamo work?
A coil is placed between two magnets, this causes the coil to spin. This induces a current in the coil. The current changes direction every half turn, but dynamos have a split ring commutator which swaps the connection to keep the current flowing in the same direction.
How does an alternator work?
A coil is placed between two magnets, this causes the coil to spin, which induces a charge in the coil. They have slip rings and brushes so the contacts don’t change every half turn.
How do microphones work?
Sound waves hit a flexible diaphragm which is attached to a coil of wire which surrounds one pole of a magnet. The diaphragm is moved back and forth by the sound wave, this generates a current in the coil.
How does a loudspeaker work?
A coil is wrapped around one pole of a magnet. A a.c signal is passed through the coil, causing it to move back and forth. This movements make a cone vibrate, causing variations in pressure that cause sound waves.
