P7- magnetism Flashcards
describe bar magnets
-they have 2 ends which are called poles.
-The magnetic forces are
strongest at the poles of
the magnet.
What happens when we bring 2 magnets close together?
they will exert a force in one of these two ways:
-repulsion= In two similar poles it is forcing the magnets apart.
eg. NN SS
-attraction= two opposite poles attract eg. NS
what are repulsion and attraction examples of
non contact forces=which means they do not touch.
describe a permanent magnet
-produces its own magenetic field
-eg. bar magnet
-If you bring 2 permanent magnets together they will either attract or repel.
describe an induced magnet
-an object that comes a magnet when placed into a magnetic field
-they always cause a force of attraction
-if we take away the permanent magnet then the induced magnets will lose their magnetism
what are electromagnets
-When we close the switch:
An electric current flows around the circuit
- and shows the conventional current.
-When a current flows through a
conducting wire, a magnetic field is produced around the wire.
how do we prove there is a magnetic field around the wire
-using a compass
-Once the current is turned on then the compass deflects.
-This proves that there is a magnetic field around the wire.
how to work out the direction
of the magnetic field produced by a wire.
using the right hand grip rule
How do you increase the strength of the magnetic
field?
number of coils
increase the current
place a piece of iron core at the centre
why are electromagnets useful
-We can change the strength of the magnetic field by changing the size of the current.
-We can turn them on or off
describe the motor effect
-A wire carrying a current creates a magnetic field
-This can interact with another magnetic field, causing a force that pushes the wire at right angles.
How do we work out the direction of the force?
flemings left hand rule
mother- motion/movement
father- force
child- current
describe electric motors
-a loop of wire carrying a current.
-the current is running in the opposite direction to the current
-The loop of wire is now in a magnetic field.
-The wire now experiences a force on both the left and right
sides.
-The loop of wire is now in a magnetic field.
-This means that the loop will rotate in a clockwise direction.
-Once the loop is at 90◦ it will stop rotating.
-imagine that the loop rotated beyond 90◦. because of the direction of the current there is a force acting upwards and downwards. These forces pushes the loop back to the 90◦ position.
-look on slide 25-30 for diagram
how do solve the rotation issue in the electric motors
-if we switch the direction of the current when the loop passes 90◦.
-To do this we use a device called a split ring commutator.
-By switching the direction of the current, the split ring commutator allows the motor to keep rotating
in the same direction.
