Topic 12: Magnetism and The Motor Effect Flashcards
12.1 Recall that unlike magnetic poles attract and like magnetic poles repel
Unlike magnetic poles attract and like magnetic poles repel. E.g North and North repel but South and North attract.
12.2 Describe the uses of permanent and temporary magnetic materials including cobalt, steel, iron and nickel
Permanent magnets are made of iron, nickel and cobalt.
Some alloys and compounds are also magnetic.
They are used for fridge doors, medical, recycling plants and many other things.
12.3 Explain the difference between permanent and induced magnets
Permanent magnets are made from permanent magnetic materials like steel.
They produce their own magnetic field all the time.
Induced magnets only produce a magnetic field when they’re in another external magnetic fields.
When it’s removed the object loses its magnetism.
12.4 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
All magnets will produce a magnetic field from the North to the South poles. The magnetic field in a bar magnet will flow around the bar from north to south in uniform and will be strongest at the poles. The closer the line are to each other the stronger the magnetic field.
12.5 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 compasses are used to find magnetic field lines.
You can find the shape and direction.
You put the magnet on the piece of paper and draw around it, then draw two dots at each end of the needle, keep moving the compass in the direction of the needle and plot the dots to get field lines.
12.6 Explain how the behaviour of a magnetic compass is related to evidence that the core of the Earth must be magnetic
When there isn’t a magnet, compasses point to the north as the earth generates its own magnetic field towards the iron core in the earth.
12.7 Describe how to show that a current can create a magnetic effect and relate the shape and direction of the magnetic field around a long straight conductor to the direction of the current
When a current flows through a long, straight conductor like a wire, a magnetic field is created around it.
It’s made up of circles perpendicular to the conductor.
This is how a current can create a magnetic field.
12.8 Recall that the strength of the field depends on the size of the current and the distance from the long straight conductor
The strength of the field depends on the size of the current and the distance from the long straight conductor.
12.9 Explain how inside a solenoid (an example of an electromagnet) the fields from individual coils
a) add together to form a very strong almost uniform field along the centre of the solenoid
b) cancel to give a weaker field outside the solenoid
A solenoid is an example of an electromagnet (turned on and off by current).
You can increase the strength of a magnetic field by wrapping the wire into a coil called a solenoid.
Inside the solenoid, lots of field lines point in the same direction so the field is strong and almost uniform.
Outside of the solenoid, a lot of the overlapping field lines cancel out so the field is weak at the end of it.
12.10 Recall that a current carrying conductor placed near a magnet experiences a force and that an equal and opposite force acts on the magnet
A current carrying a conductor placed near a magnet experiences a force and that an equal and opposite forces acts on the magnet.
12.11 Explain that magnetic forces are due to interactions between magnetic fields
Forces between magnets are caused by interacting magnetic fields.
When 2 poles are near each other, the magnetic lines overlap and cancel each other out.
The reaming fields push the 2 poles apart.
This is when they repel.
When they attract, a uniform field is created which pulls the two poles together.
12.12 Recall and use Fleming’s left-hand rule to represent the relative directions of the force, the current and the magnetic field for cases where they are mutually perpendicular
Fleming’s left-hand rule - represents relative directions of force, magnetic field and current.
(see image)
12.13 Use the equation:
force on a conductor at right angles to a magnetic field carrying a current (newton, N) = magnetic flux density (tesla, T or newton per ampere metre, N/A m) × current (ampere, A) × length (metre, m)
F=B×I×l
Equation for force on a conductor:
- force on a conductor at right angles to a magnetic field carrying a current
(newton, N) = magnetic flux density (T or N/Am) × current (A) × length (m)
F=B×I×l
12.14p Explain how the force on a conductor in a magnetic field is used to cause rotation in electric motors
When a conductor is carrying current in a magnetic field then the conductor will experience a force.
This is the ‘motor effect.’
Electric motors use a loop of wire which means that the current running through will run in opposite directions at opposite sides of the loop.
When the wire is in a magnetic field the wire will experience opposite forces on opposite sides. Therefore the wire will rotate.
