What does an electric current in a conductor produce?
an electric current in a conductor produces a magnetic field around it
What is the relatonship between electric current and the magnetic field?
the larger the current, the stronger the magnetic field
What does the direction of the magnetic field depend on?
the direction of the magnetic field depends on the direction of current
What is exerted on a current-carrying wire in a magnetic field?
force is exerted on a current-carrying wire in a magnetic field
What is the relationship between the force exerted on a current-carrying wire in a magnetic field and the strength of the field and the current?
the force exerted on a current-carrying wire in a magnetic field increases with the strength of the field and the current
The magnitude (strength) of a force increases with the strength of the magnetic field
The magnitude (strength) of a force increases with the amount of current passing through the conductor
What happens when a current-carrying wire is put between magnetic poles?
when a current-carrying wire is put between magnetic poles, the two magnetic fields affect one another
the result is a force on the wire which can cause the wire to move
Why does a current-carrying wire move when put between two magnetic poles?
charged particles (e.g. electrons in a current) moving through a magnetic field will experience a force, as long as they are not moving parallel to the field lines
How does a current-carrying wire expereince full force?
the wire has to be at 90o
What happens if a current-carrying wire runs along the magnetic field? What about at angles in between?
a current-carrying wire running along the magnetic field won't experience any force at all
a current-carrying wire running along the magnetic field at angles in between will experience some force
How do you reverse the direction of the force?
reversing the current or the magnetic field also reverses the direction of the force
Sketch the magnetic field patters for a straight wire
the field is made up of concentric circles with the wire in the cntre
Sketch the magnetic field patters for a flat ciruclar coil
the magnetic field in the centre of a flat circular coild of the wire is similar to that of a bar magnet
there are concentric ellipses (stretched circles) of magnetic field lines areoung the coil
(the brown line is the current)
Sketch the magnetic field patters for a solenoid
the magnetic field inside a current-carrying solenoid (a coil of wire) is strong and uniform
outside the coil, the field is just like one around a bar magnet
this means that the ends of the solenoid act like the north pole and south pole of a bar magnet
this type of magnet is called an electromagnet
What is a solenoid?
How do you make an electromagnet
electromagnets are magnets made by wrapping a coil of wire around an iron bare and passing an electric current through the coil
How do you make an electromagnet stronger?
wrapping the coil around an iron core
adding more turns to the coil
increasing the current flowing through the coil
increasing the voltage of the power supply
bounding the coiled wire more tightly
Can magnetic field lines cross?
magnetic field lines cannot cross each other - they interact
What does Fleming's Left-Hand Rule tell you?
Fleming's Left-Hand Rule tells you the direction of the resulting force when a wire carries a current perpendicular to a magnetic field
it tells you which way the force acts
How do you use Fleming's Left Hand Rule?
using your left han:
point your first finger in the direction of the field
point your second finger in the direction of the curent (current will go from north to south)
your thumb will point in the direction of the force (motion)
How do you speed up an electric motor?
increasing the current
more turns on the coil
bound the coil more tightly
stronger magnetic field
adding a soft iron core in the coul
How do loudspeakers work?
loudspeakers work because of the motor effect
alternating current (a.c.) signals from an amplifier are fed to a coil of a wire in the speaker, which is wrapped around the base of a cone
the coil is surrounded by a permanent magnet, so the a.c. signals cause a force on the coil and make it move back and forth
these movements make the cone vibrate and this creates sound
What is current?
a flow of electrons
What does a d.c. motor do?
a d.c. motor converts electrical energy into useful kinetic energy
What does the split ring commutator do in a d.c. motor? What would happen without it?
changes the direction of the current every half
without it, the motir would rotate to the vertical position and then vibrate until it came to rest
Magnetic fields flow from ... to ...
Magnetic fields flow from North to South
At what angle does the force of the coil act in a d.c. motor?
the force on the coil acts at right angles to the permanent magnetic field
Where does the coil rotate in a d.c. motor?
it rotates in the permanent magnetic field
What does the battery do in a d.c. motor?
converts chemical energy to electrical energy
What are the brush contacs in a d.c. motor made of? Why?
made of graphite (carbon) because it is a good conductor and is soft - therefore reducing friction between it and the split ring commutator
Why does the wire on the left side of the coil in an electric motor experience an upward force whilst the wire on the right experiences a downward force?
the current is flowing in the opposite direction
In an electric motor, what happens to the current when the coil is vertical? Why?
the current no longer flows because there is a gap between the split ring commutator and the rush contacts
at this point there is no force acting on the coil because there is no current flowing
Why does the coil in a d.c. motor continue to rotate even when there are no forces acting on the it?
it has momentum
Label this d.c. motor
What is the easiest way to make an electromagnet?
when a current flows through a conductor, a magnetic field is produced around the conductor - you now have an electromagnet