Magnetism Test Flashcards
Magnets have two poles…
North (or north seeking) and South (or south seeking)
There are two types of magnets…
Permanent and Induced
Permanent magnets…
Produce their own magnetic field
Induced magnets…
Are magnetic materials that turn into a magnet when placed in a magnetic field
The force between permanent and induced magnets are…
Always attractive
When the magnetic field is taken away, induced magnets…
Lose most or all of their magnetism
When a current is flowed through a wire…
A magnetic field is created around the wire
The magnetic field of a wire is made up of…
Concentric circles perpendicular to the wire that is carrying the current
Changing the direction of the current…
Changes the direction of the magnetic field
The Right-Hand Thumb Rule is…
Using the right hand to find the direction of the field by:
- Pointing the thumb in the direction of the current
- Curling the other fingers into the palm of the hand
- Finding the direction of the field by following the root of the fingers to the tips
The strength of the magnetic field produced by a wire changes…
With the current and distance from the wire. More current and less distance = stronger field, less current and more distance = weaker field
A solenoid…
Is a coil of wire
The strength of the field of the wire can be strengthened even further by…
Wrapping the wire into a coil
The strength of a solenoid is greater than that of a straight wire because…
Each loop of the wire line-up with each other resulting in lots of field lines pointing in the same direction which are very close together
The magnetic field inside a solenoid is…
Strong and uniform (same strength and direction at every point in that region)
The magnetic field outside a solenoid is…
Just like that of a typical bar magnet
The field strength of a solenoid can be strengthened by…
Placing an iron core in the centre of the coil which makes the iron core an induced magnet
When a current is no longer present in a wire…
The magnetic field disappears
A solenoid with an iron core is…
An electromagnet
An electromagnet is defined as…
A magnet that can be turned on and off with an electric current
Electromagnets can be used within circuits as…
Switches
The motor effect is…
When a conductor (e.g current-carrying wire) is put between magnetic poles, the magnetic field around the wire interacts with the magnetic field it has been placed in; causing the magnet and the conductor to exert a force on each other
To experience the full-force of a magnetic field…
The wire has to be perpendicular to the magnetic field
The force of a magnetic field always acts
At right angles
The magnitude (strength) of the force…
Increases with the strength of the magnetic field and the amount of current passing through the conductor
The force acting on a conductor in a magnetic field depends on three things…
Magnetic flux density, size of current and the length of the conductor that’s in the magnetic field
The magnetic flux density is…
The amount of field lines there are in a region, showing the strength of the magnetic field
Fleming’s Left-hand rule is…
- Using the left hand and pointing the first finger in the direction of the field (First - Field)
- Point the second finger in the direction of the current (seCond - Current)
- The thumb will then point in the direction of the force (thuMb - Motion)
A current-carrying coil of wire…
Rotates in a magnetic field
If the coil is on an axle…
The forces act one up and one down, causing it to rotate
The direction of the motor can be reversed by…
Reversing the current or by reversing the field
The direction of the coil’s turn can be found with…
Fleming’s left-hand rule
Electricity is generated by…
Using the generator effect
The generator effect induces…
A potential difference in a conductor and a current if the conductor is a part of a complete circuit
You can create the generator effect by…
Moving a magnet in a coil of wire or moving a conductor (e.g wire) in a magnetic field
If the magnet or conductor is moved in the opposite direction…
The potential difference and current will be reversed
If the magnet keeps moving backwards and forwards…
A potential difference is produced that keeps swapping direction which is called an alternating current
The generator effect can be replicated by…
Turning a magnet end to end in a coil, or turning a coil inside a magnetic field. This is how generators produce alternating current (ac) or direct current (dc)
As the magnet turns…
The magnetic field through the coil changes, introducing a potential difference which can make a current flow within the wire
Every time the magnet moves through a half turn…
The magnetic field of the coil and the potential difference reverses. This causes the current to flow the opposite direction
If the magnet is turned in the same direction continuously…
The potential difference will keep reversing and a alternating current will be produced
The magnetic field created by an induced current…
Always acts against the change that made it. Or in other words: it’s trying to return things to the way they were
Alternators…
Generate alternating current
Dynamos…
Generate direct current
The construction of alternators and dynamos are similar…
To the construction motors
Alternators use slip rings and brushes…
So that the contacts don’t swap every half turn
Dynamos use split-ring commutator instead of slip rings because…
They swap the connections every half turn to keep the current flowing in the same direction
