P7-Magnetism and Electromagnetism Flashcards
What makes an object magnetic?
The domains can line up-the molecules’s electrons spin in the same direction
What poles attract?
What poles repel?
- Opposite
- Same
What are the magnetic materials?
Iron, Cobalt and Nickel
What is a magnetic field?
The region around a magnet
What is a permanent magnet?
A magnet that always produces a magnetic field and can’t be turned on or off
What is an induced magnet?
A magnet that can be magnetised when placed in another magnetic field
What are the characteristics of magnetic field lines?
- Travel from north to south poles
- Are more concentrated at the poles than elsewhere
- Never cross-only loop around
- Form rings
What direction does a current flowing through a wire produce its own magnetic field when veiwed from the direction the current is flowing and what tells us that the current is facing that direction on a diagram?
- Clockwise
- A cross
What direction does a current flowing through a wire produce its own magnetic field when veiwed from the the direction the current isn’t flowing and what tells us that the current is facing that direction on a diagram?
- Anti-Clockwise
- A dot
What direction does a current flowing through a wire produce its own magnetic field?
Clockwise-right hand rule
What is a solenoid and what does it produce?
A long coil of insulating wire-it produces a magnetic field
What is an electromagnet?
A soleniod with an iron core
What increases the strength of an electromagnet?
- Increasing the current
- Increasing the number of coils
What is the motor effect?
A wire carrying a current that creates a magnetic field that interacts with another magnet to cause a force that pushes the wire at right angles
How can the size of the motor effect force be increased?
- By increasing the current
- By using a stronger magnet
- By increasing the length of the wire
How do you use Fleming’s left hand rule?
Thumb-Force
1st finger-Magnetic field
2nd finger-Current
What is the formula for force on a wire in a magnetic field?
Force = magnetic flux density x current x length
F = BIL
What are the units for magnetic flux density?
tesla, T
What is magnetic flux density?
The strength of the magnetic field
What causes the motor to keep spinning in the motor effect?
A split-ring commutator
What current is used in an electric motor?
Direct current
What can cause a current to be generated and what is this called?
A coil of wire being moved in relation to a magnet-this creates an induced current-called the generator effect.
What factors reverse the current generated from a magnet?
If the magnet is moved back out of the coil
If the other pole of the magnet is moved into the coil
How does an AC generator work?
A coil is rotated in the magnetic field inducing a current and brushes making contact between this wire and an external circuit causes an alternating current to flow in the external circuit
How can the maximum current be increased in an AC generator?
- Increasing the rate of rotation
- Increasing the strength of the magnetic field
- Increasing the number of turns on the coil
How is a DC current produced by a generator?
What is the name for this generator?
- By having a split ring commutator-however this produces a ‘lumpy’ current
- Dynamo
What do transformers do?
- The increase the size of the voltage of an alternating current (step up transformer) while reducing the current)
- They decrease the size of the voltage of an alternating current (step down transformer) while increasing the current)
What causes a step up transformer?
If there are more turns in the secondary coil
How do transformers work?
- An AC power supply is supplied to the primary coil-this produces a magnet field that changes as the current changes
- The iron core increases the strength of the magnetic field
- The changing magnetic field induces a changing potential different in the secondary coil
- The induced potential difference produces an alternating current in the electric circuit
