P15: Magnetism Flashcards
Where are the poles of magnets?
The places where the magnetic forces are strongest
What is the difference between a permanent magnet and an induced magnet?
A permanent produces its own magnetic field whereas an induced is a material that becomes a magnet when it is placed in a magnetic field.
What do induced magnets always cause?
A force of attraction
What are the 4 magnetic materials?
Iron, steel, cobalt and nickel
What is a magnetic field?
The region around a magnet where a force acts on another magnet or another magnetic material
What does the strength of a magnetic field always depend on?
The distance from the magnet
When is a magnetic field produced around a conducting wire?
When a current flows through it
What 2 things does the strength of a magnetic field around a conducting wire depend on?
The current through the wire and the distance from the wire
What pole does the field lines come out of a bar magnet?
North
What are the 4 ways you can increase an electromagnetic strength?
Increase the current that flows, increase the number of turns in the coil (for the same length of coil), decrease the length of the coil (for the same number of turns) and add an iron core on the inside, becoming an induced magnet.
Describe the magnetic field in a solenoid in two ways
Strong and uniform
What does the motor effect state?
A current-carrying wire in the presence of a magnetic field will experience a force.
What is the formula to calculate the strength of a force?
Force = magnetic flux density x current x length of wire
What does a split-ring communtator do?
It swaps the negative and positive connections every half turn, so that the direction of the current is also swapped and the forces acting on the coil will always be acting in the same direction
How can the speed of rotations in an electric motor be increased?
Increase current, add more turns in coil, and increase magnetic flux density by using more powerful magnets
In the generator effect, how can the size of the induced potential difference be changed?
Change the strength of the magnetic field (stronger magnet), move wire/magnet more quickly and shape the wire into coil to have multiple turns, causing a bigger induced PD
What shows the strength of a magnetic field?
The density of the magnetic field lines
What is a magnetic material?
A material or object that can be influenced by a magnetic field and has the potential to become a magnet
When will a wire not feel a force?
When it is pointing in the same direction as the magnetic field
When a wire is induced in a magnetic field and is moved up and down, why does the potential difference disappear when it stops?
Because its the change in the magnetic field that the wire experiences as it moves through it that creates the potential difference
What are 3 things that can be done to change the size of the induced potential difference in the generator effect?
Change the strength of the magnetic field, move the wire or magnet more quickly and shape the wire into a coil
What current do dynamos produce?
Direct
How does an alternator work?
The coil rotates which induces a magnetic field in it. It induces a voltage and current in the coil. The slip rings and brushes ensure there is no swapping every half turn, producing an alternating current
How do dynamos work?
The coil spins relative to the magnet, inducing a voltage and a current. The split ring commutators allow swapping every half turn. This means a direct current is produced
What is the difference between loudspeakers and microphones? What are similarities?
Loudspeakers use the motor effect and microphones use the generator effect. They both involve alternating currents
How do loudspeakers work?
An alternating current flows, causing a magnetic field to appear. This interacts with the permanent magnet’s field, and the interacting fields exert a force on the coil causing it to move back and forth along permanent magnet. This causes the cone to change shape and the magnetic field and force also alternate so vibrations are formed from the moving back and forth. The vibrations are so fast that sound waves are produced
How do microphones work?
Sound waves hit the diaphragm and this causes it and the coil to move. The wire will generate a current as it moves in the permanent magnet’s field. The frequency and amplitude of soundwaves determine that of the current
How do transformers work?
When supplied with an a.c, the primary will generate an alternating magnetic field, which induces an alternative magnetic field in the iron core. This induces an alternating voltage in the secondary which will lead to an a.c. if the circuit is complete
What are the 2 equations used for transformers?
Vp/Vs = Np/Ns and VpIp = VsIs
