Topic 12 - Magnetism and the Motor Effect Flashcards
12.1 - What do magnets have?
Magnets have poles which when same repel and when opposite attract.
12.2/3 - Describe what permanent and temporary magnets are
Permanent magnets such as bar magnets are always magnetic.
Temporary or induced magnets such as steel, nickel, iron and cobalt all become magnetic when it is in the area a permanent magnet can attract it which is a magnetic field.
12.2 - Describe the uses of permanent and temporary magnetic fields
Magnets are used in electric motors, generators and loudspeakers.
12.4 - Describe a magnetic field around bar magnets
Magnets usually have uniform magnetic fields and has the same strength and direction everywhere.
12.5 - Describe how to show the shape of a magnetic field
By plotting compasses, you can represent the magnetic field by using lines to show the north pole.
12.6 - Explain to show evidence the Earth’s core is magnetic
Compasses have needles that always point the Earth.
The behaviour of compasses is evidence that Earth has a magnetic field in the shape similar to a bar magnet.
Earth’s outer core is caused by a mixture of iron and nickel.
12.7 - Describe how current can create a magnetic effect
When current moves through a long straight conductor it causes a magnetic field.
The magnetic field is circular around the wire and can be draw using plotting compasses.
If the direction of current changes, so does the direction of the magnetic field.
The thumb rule can be used to show this magnetic field by pointing the thumb in the direction of current the direction of fingers shows the magnetic field.
12.8 - What does the strength of the magnetic field in a wire depend on?
The higher amounts of the current in the wire makes the field stronger.
The field is stronger closer to the wire and loses strength as the distance decreases.
12.9 - Explain what a solenoid is
A solenoid is a wire made into a coil.
When this happens the magnetic fields from all the parts of a wire form an overall magnetic field.
This is because the fields from the individual coils add to make a very strong field inside.
Outside the solenoid, the field from the top and bottom of the solenoid cancel out, while in the middle of the solenoid the field is reinforced as they overlap.
12.9 - What type of magnet is a solenoid?
An electromagnet is a coil of wire with a current flowing through it.
The magnetic field in the electromagnet can be made stronger by placing iron in it to make it a temporary magnet and increase the field strength.
12.10/11 - What happens when a wire carrying a current is placed between two magnets?
The field around the wire interacts with the field between the magnets.
The force is greatest when the wire is perpendicular to the one another.
The force is zero when in the same direction as one another as there is an equal and opposite force.
12.12 - Explain Fleming’s left hand rule
Force is shown with the thumb.
Magnetic field shown by index.
Current shown by middle.
12.13 - What equation links force, magnetic field strength, current and length?
F = BIL
Newtons = Teslaampsmetre
12.14P - Explain how electric motors work
Current goes from the negative to positive terminal and when moving away force is upwards.
When moving towards the force is downwards.
When moving clockwise the current changes and pair with the opposite terminals. This makes it turn anti-clockwise going back to how it was.
To fix this, direction of current changes so the coil rotates in the same clockwise direction.
Split ring commutator swaps positive and negative terminals every half turn, this means the current also swaps every half turn.
So forces on coil is always in same direction.
Carbon brushes make electrical contacts between circuit and motor.
