Chapter 12 Flashcards
Explain difference between permanent and induced magnets
Bar magnets are permanent magnets. This means their magnetism is there all the time and cannot be turned on or off as it can with electromagnets.
A magnet that only acts as a magnet when in a magnetic field is called an induced magnet
Give examples of substances that can be permanently magnetised
They are described as magnetically hard. These are often alloys of iron, nickel and cobalt.
List magnetic metals
Iron, Nickel, colbalt and steel as its an alloy of iron
Give example of substances that can only be temporarily magnetised
They are described as magnetically soft. Alloys with less iron, nickel or cobalt will be magnetically soft with a weaker magnetic field. Alloys of iron are called ferrous and those without it are called non ferrous
describe an electromagnet
When an electric current flows in a wire it creates a magnetic field around the wire. By winding the wire into a coil we can strengthen the magnetic field .
How can we strengthen the electromagnet
wrapping the coil around an iron core
adding more turns to the coil
increasing the current flowing through the coil
Describe the uses of permanent and temporary magnetic materials including cobalt, steel, iron and nickel
aircraft applications such as compass, generators, starter motors and navigation.
permanent magnet= fridge magnet
temporary magnet= doorbells and complex objects such as motors
Describe the shape and direction of the magnetic field around
bar magnets and for a uniform field, and relate the strength of
the field to the concentration of lines
A uniform field= same strength and direction between 2 magnets
Ununiformed field= Direction goes North to South. Field lines stronger closer to the magnet
Describe the use of plotting compasses to show the shape and
direction of the field of a magnet and the Earth’s magnetic
field
Plotting compass needle is a tiny magnet. It points north. This behaviour is evidence that the Earth has a magnetic field.
Explain how the behaviour of a magnetic compass is related to
evidence that the core of the Earth must be magnetic
The Earth’s magnetic field exists because of electric currents in the molten outer core which is made from a mixture of iron and nicke
Describe how to show that a current can create a magnetic
effect around a long straight conductor, describing the shape
of the magnetic field produced and relating the direction of the
magnetic field to the direction of the current
A wire carrying an electric current produces a magnetic field. The shape of this field depends upon the shape of the wire.
The magnetic field around a straight wire consists of concentric circles (circles around the same centre). There are at right angles to the direction in which the electric current flows.
What does the strength of the field depend on
size of the current and the distance from the long straight conductor
What is a solenoid
A coil of current carrying wire. This produces a magnetic field, which is increased if a soft iron core is placed inside. Solenoids, especially when a soft iron core is placed inside, can be used as electromagnets
What does a current carrying conductor experience when placed near a magnet
it experiences a force and an equal and opposite force acts on the magnet
What are magnetic forces due to
interactions between magnetic fields
How is the force on a conductor in a magnetic field used to cause rotation in electric motors
Electric motors use the motor effect. A simple electric motor consists of a coil of wire that is free to rotate between 2 opposite magnetic poles. When an electric current flows through the coil, the coil experiences a force and moves. One side moves up whilst the other side moves down (based on flemmings left hand rule)
What is the equation including force, magnetic flux density, current and length
F= B X I X L
BIL
what happens inside a solenoid wen the fields from individual coils add together
the fields from individual coils add together to form a very strong almost uniform field along the centre of the solenoid
what happens inside a solenoid when the fields from individual coils cancel
the fields from individual coils cancel to give a weaker field outside the solenoid
what is a concentric magnetic field
circles which share the same centre, perpendicular to the wire. The strength of the field depends on size of current and distance from wire
when current flows through a wire what is created
a concentric magnetic field
