Magnetism Flashcards
What poles attract each other
N-S
S-N
What poles repel each other
N-N
S-S
What materials are magnetic
Cobalt
Nickel
Iron
Steel
What is a permanent magnet
A magnet that produces its own magnetic field
What is an induced magnet
A temporary magnet that only becomes magnetic when it’s in a magnetic field
How would you know if a block is a permanent magnetic
The block will attract an repel another magnet and it will always attract magnetic material
How do you draw a magnetic field
Place the plotting compass near the magnet on a piece of paper
Mark the direction the compass needle points
Move the plotting compass to many different positions in the magnetic field, marking the needle direction each time
Join the points to show the field lines
Repeat this until you have a couple more field lines
What is a solenoid
A wire coiled up in a spiral shape
Has the magnetic filed of a bar magnet
What is an electromagnet
A solenoid with an iron core which can be turned on or off
What is the equation linking force, magnetic flux density, current and length
F = BIL
F - force, measured in newtons (N)
B - magnetic flux density, measured in tesla (T)
I - current, measured in amps (A)
L - length, measured in metres (m)
How do you use the left hand rule used for
Point your index finger in the direction of the magnetic field. Point your middle finger in the direction of the current. Point your thumb up and that is the direction of the current
How do you use the right hand rule
You put you right hand in a thumbs up position and point your thumb in the direction of the current
How does the motor effect work
Current in the left hand part of the coil causes a downward force, and current in the right hand part of the coil causes an upward force
The coil rotates anti-clockwise because of the forces described above
When the coil is vertical, it moves parallel to the magnetic field, producing no force. This would tend to make the motor come to a stop, but two features allow the coil to continue rotating:
The momentum of the motor carries it on round a little
A split ring commutator changes the current direction every half turn
Once the conducting brushes reconnect with the commutator after a half turn:
Current flows in the opposite direction through the wire in the coil
Each side of the coil is now near the opposite magnetic pole
What are the two transformers
Step up - increase voltage
Step down - decrease voltage
