what is the region around the magnet called
magnetic field
what are permanent magnets
they produce their own magnetic field
what are
... [Show More] induced magnets
become a magnet when placed in a magnetic field
what way do the arrows on field lines run
north to south
what is the flux density
the density of the field lines - it indicates the strength of the field at that point (the closer the lines the higher the flux density = stronger the field and greater the force)
what does the compass needle align with and what direction does it point
the Earth's magnetic field and points to the magnetic north
how can a magnetic compass be used to plot the field around a bar magnet
place the bar magnet on a piece of paper
place the compass at one end of the magnet
mark on the paper where the point of the compass needle is
move the compass so the tail of the needle is at the point that has just been marked
mark on the paper a new point where the needle is
repeat and connect the marks until the full field is plotted
what happens when a current flows in a conducting wire
a magnetic field is produced around the wire
what does the direction of the field lines depend on
the direction of the current and can be found with the right hand grip method
demonstrate the right hand grip method
grip the wire in your right hand, with the thumb pointing in the direction of the current
the fingers curled around the wire will point in the direction that the field lines should be drawn
what does the strength of the field depend on
the size of the current and the distance from the wire
how is a solenoid formed
when a wire is looped into a cylindrical coil
how can you increase the strength of the magnetic field
shape the wire into a solenoid - will increase the strength because it conc. a longer piece of wire into a smaller area, the loop shape means the magnetic field lines are all in the same direction
add an iron core
how can the north pole of a solenoid be found with the right hand grip method
hold the solenoid in your right hand with you fingers following the direction the current flows
your thumb will point to the north pole of the solenoid
how does the electromagnetic device of an electric bell work
when the with is pushed, the electromagnetic is magnetised
the electromagnet attracts the armature
the hammer strikes the gong and breaks the circuit
the armature springs back, completing the circuit again and demagnetising the electromagnet
the cycle repeats for as long as the button remains pushed
what is the motor effect
when a current carrying conductor is placed in a magnetic field it experiences a forced (the motor effect)
what is the motor effect caused by
the field created by the current interacting with the magnetic field
how can the force be increased
by increasing either the size of the current, the length of the conductor or the flux density
what is the equation for force
force = magnetic flux density (T) x current x length of the wire within the field
what happens if the current or magnetic field is reversed
the direction of the force is reversed
how can the direction of the force be found using Fleming's left hand rule
hold the left hand so that the thumb, first finger and second finger are all at right angles to one another
align the first finer, so that it points in the direction of the magnetic field from north to south
rotate the wrist so that the second finer points along the wire in the direction that the current is flowing
the thumb will be pointing in the direction of the force - the direction the conductor would move
what are the conditions for the left hand rule to work
can be used to find the direction of the field / current / movement as long as the other two are known
a current carrying coil in a magnetic field will...
rotate
why?
the current going up one side of the coil I in the opposite direction to the current coming back down the other side, so one side moves up and the other move down
basis of an electric moron - continuously rotating coil
how do loudspeakers and headphones produce sound waves
they use the variations in an alternating current to produce sound waves
loudspeakers
as the current travels through the coil, it experiences a force due to the magnetic field, this makes the speaker cone move
because the current is alternating, the direction of the force alternates and speaker cone oscillates
increasing the electrical power will produce a larger force - the cone will oscillate with a higher amplitude and produce louder sound waves
the frequency of the sound produced matches the frequency of the alternating current
the size of the speaker affects how quickly or slowly it can oscillate and how big these oscillations will be
a large cone is better for low pitched sounds and a small cone is better for high pitched sounds
what is the generator effect
when conductors and magnetic fields interact, a potential difference is induced (the generator effect)
how can this potential difference be induced
an electrical conductor moving relative to a magnetic field
a change in magnetic field around a conductor
what will increasing the speed of the movement or magnetic field increase the size of
the induced potential difference
what will reversing the direction of the movement or magnetic field do
reverse the direction of any induced current
what does an induced current generate
a magnetic field that opposes the original change or the change in magnetic field
wha is the generator effect used in
alternators to generate an alternating current
dynamos to generate a direct current
what happens as the magnet rotates
the direction of the field through which the coil passes alternates - this induces an alternating potential and an alternating current
what happens in a dynamo
the coil rotates and the magnet is fixed. as the coil rotates it generates a potential difference in one direction
what does the use of the split-ring commutator mean
once the coil has passed the upright position, the connections are reversed - as a result the direction of the current output is always in the same direction
in both cases, the induced potential difference is greatest when the magnet field and the coil are parallel, so the magnetic field is being 'cut' by the rotating coil at the fastest rate
in both cases, the induced potential difference is greatest when the magnet field and the coil are parallel, so the magnetic field is being 'cut' by the rotating coil at the fastest rate
for alternators, what is the frequency of the alternating current
the speed of rotation
a moving coil microphone uses the generator effect to convert sound waves into electrical signals
the sound waves hit the microphone
the changes in air pressure related to the sound wave cause the microphone diaphragm to oscillate
the microphone diaphragm and coil vibrate at the same frequented as the incoming sound wave - the bigger the amplitude of the sound, the bigger the amplitude of the vibration
this induces a potential difference on the amplitude of the incoming wave
what does a basic transformer consist of
a primary and secondary coil wrapped around a soft iron core
what is the function of a transformer
an alternating current flows through the primary coil, which is effectively a solenoid
this alternating current induces an alternating magnetic field
the alternating magnetic field in the iron core induces an alternating potential difference in the secondary coil
if the secondary coil is part of a complete circuit, an alternating current flows in the secondary coil
what would happen if transformers were 100% efficient
the power output would be the same as the power input
what is the equation for power
voltage x cutest (when the potential difference is increased, the current is reduced and vice versa
voltage equation
voltage (primary number of turns (primary)
over = over
voltage (secondary number of turns (secondary)
voltage (secondary) x current (secondary) = voltage (primary) x current (primary) [Show Less]