P4.1 Flashcards
What is magnetic flux density
The strength of the magenetic field is measured in Tesla’s. More field lines that cut an area, the more flux
What is a magnetic field
What are
Properties of it
What are permanent vs induced magnets
A field where magnetic material (iron, nickel or cobalt) experiences a force
Closer the stronger.
Permanent magents have their own field and can attract and REPEL another permanent magnet. Induced ones become magnets but lose magnetisier when magnet is moved away. It can only attract be attracted to a permanent magnet, and if you flip the domains readjust and still attracted , never repel.
What is domain model and how does that explain induced magnets
A magnet is made up of small regions the line up. In a non permanent magnet, these lines do not line up, or some of them do, but when put in the field of a permanent magnet, more of their domains line up, making them a temporary but induced magnet. If the magnetic material is strong, some of the domains will continue to stay aligned even after the magnet is removed…
But most will be unaligned and so loses magnetism
This is how paper clip is attracted to magent( it is stell so has iron, domain theory )
How do you model magnetic field lines,
1) with iron fillings. Simply place a magnet under a
Jede of paper and scatter some of the iron fillings on top- they will form the field lines.
2) you can do it with a plotting compass too. Place a magnet on a piece of paper and a compass any where around it. The compass needle should point in the direction of a field line at this position. With a pencil, Mark the top and bottom of the needle. Then , move the tail end of the needle to where the tip was before, and repeat
- connect and draw the marks you have made- you should now have a field line. Repeat this around the magnet to get more field lines..
Why use a compass to show field lines rather then fillings.
3) a compass is better then iron fillings because 1) after the magnet is removed the drawings of the field lines remain, whereas an iron fillings leave. 2) iron fillings are messy and can be hard to separate if they stick to the magent.
3) It also shows DIRECTION OF FIELD LINES
Earth magent and compasses
What is the ‘dip’ of countries?
A compass will always point to north when not in the presence of a magnetic field. Compasses have to be weighted horizontally or they won’t work…
1) this in fact is earth’s magnetic south , but geographic earth. The earth has its own magnetic field because of the CONVECTION CURRENTS in the molten core of earth (molten iron and stuff) (Scientist don’t know for a fact)
The angle between the field lines (north) and a straight line on earth surface (equator?) this is 70° In uk but in North Pole 90°
A current flowing through a wire will produce a magnetic field,
What does this look like
How does strength increase
It is concentric circles getting further apart . Find out using right thumb
Larger current + less distance from wire
Magnetic field around a flat circular coil
Magnetic field around a Solenoid + what is this?
How does a solenoid increase its magnetic field
Like a bar magnet
2) It also becomes into a bar magnet, with a south and north. Use right hand rule. A solenoid is more wires wrapped around. Mae this magnet an induced one by adding a core- it is now electromagnet which can be stronger then any other magnet…
1) increase current
2) make core iron
3) increase number of coils
4) increase area of cross section of core
5) decrease length but maintain coils
Common sense
What does a magnetic fields direction show at any point
The force direction on a North Pole (what would happen to a North Pole)
What direction is magnetic field in circular coil
Use right hand but then also it’s going through the centre
