Magnetism P4 Flashcards
What makes a permanent magnet and an induced magnet
A permanent magnet produces its own magnetic field
An induced magnet is a material that becomes a magnet when placed in a magnetic field eg: paper clip
Induced magnetism always causes a force of attraction
When removed from the magnetic field an induced magnet losses most it’s magnetism
What happens to domains before and after magnetisation
Before domain points are in random directions
After domains all point to the same direction
You can magnetise the material by stroking it with a permanent magnet
How can you use iron filings to see magnetic field lines
Put a piece of paper over a magnet to stop filings from sticking to the magnet
Sprinkle iron filings onto the paper
Gently tap the paper to spread the filings
Observe and record information
How can you use a plotting compass to mark field lines
First place a magnet on a piece of paper
Place the compass near the end of the magnet
Mark the position that the compass points to
Move the compass so the opposite end is at this new point and mark each new position
Repeat this above and below the magnet until the field lines connect together
What’s Flemings left hand rule
Thumb - Force
First finger - magnetic field line
Second finger - for current
Whats the corkscrew rule and hand applied on
Right hand
Put the thumb in the direction of the current and the fingers direction tells you the magnetic field lines around the wire
How to increase magnetic field strength
Increase current
Increase the number of coils
Put an iron core in the solenoid
Explain the motor effect
When a wire that has a current sent through it is put in a magnetic field the wire moves (the force is greater if the current is increased, a stronger magnet is used or if a coil is used) this will cause the wire to move further
Direction of the force can be reversed if the magnetic field is reversed or current is reversed
How does an electric motor work
Current in the coil creates a magnetic field around the coil
This interacts with the magnetic field of the magnet causing a force on the coil
The split ring commutator reverses the current in the coil every half turn to keep it rotating
The current flows in different directions on each side of the coil (so each side experiences the opposite force causing it to spin)
What is the generator effect
If a wire cuts through a magnetic field line a PD is induced across the wire causing a current to flow in the wire
More current is induced if a stronger magnet is used, the wire is moved faster or more wire is used (coils)
Direction is reversed if the magnetic field line is reversed or direction wire cuts through is reversed
What’s an AC and DC current
AC is alternating current meaning it is constantly changing (uses a slip ring commutators)
DC is direct current meaning it always flows in the same direction (split ring commutator swaps the direction every half turn to keep current in the same direction
What is a transformer
Transformers are used to change the PD. It consists of 2 wires wound around a soft iron core
A step down transformer has less turns at the secondary coil than primary (therefore output voltage decreases compared to input voltage)
How does a transformer work
A pd is applied to the primary coil causing an alternating current to flow in the primary coil
This alternating current causes a changing magnetic field in the soft iron core
The wires of the secondary coil then cut through the magnetic field this induces a PD across the secondary coil
How could you build a step up transformer
First get an iron core and wrap a wire around the primary part 10 times and secondary part 20 times
Put an ac current through this wire to induce a PD and create an alternating magnetic field
Then on the secondary coil it will continue to keep cutting through the alternating current which will step up the output voltage by 2 as there is double the amount of coils on secondary coil
How does a microphone work
Particles hit the diaphragm and cause it to move which moves a wire coil back and forth over a magnet
A current is induced in the coil and sends the sound waves down the wire
