3- Keeping Things Moving Flashcards
What is a magnetic field?
The region around the magnet which will attract a piece of iron or steel
What is a magnetic field line/line of force?
Iron fillings placed near a magnet form a pattern of lines that loop from one pole to the other.
Compasses point along the field line
What is an electromagnet?
Insulated wire wrapped around a piece of iron (the core)
When a current flows through the wire, the iron becomes strongly magnetised because of the magnetic field produced by the wire
Why are electromagnets useful and give examples?
Their magnetism can be controlled - temporary magnetism
Examples include: scrapyard cranes, circuit breakers, electric bells, relays
What is the motor effect?
The force experienced by the wire when it carries an electric current in a magnetic field - at maximum of the wire is at 90* to the magnetic field (does not work when parallel)
What does Flemings left hand rule determine and what does each finger mean?
The direction of the force.
The first finger: the magnetic fields direction
The second finger: the currents direction (swearing finger)
The thumb: the direction of the force
How can the size of the motor effect force be increased?
Increasing the magnetic fields strength
Increasing the size of the current
How can the direction of the motor be reversed?
Reversing the direction of the current
Why does the coil spin in a motor when the current passes through it?
A force acts on each side of the coil (motor effect)
The force on one side of the coil is opposite to the force on the other
What does a split ring commutator do in a motor?
Reverses the direction of the current around the coil every half term because of the sides swapping
What are magnetic poles?
The ends of the magnet, one is North, one is South
Opposites attract and like poles repel
What happens if an electrical conductor cuts though magnetic field lines?
Potential difference is induced across the ends of the conductor
What is electromagnetic induction?
A magnet moves into a coil of wire inducing potential difference across the ends of the coil
How do you reverse the direction of the induced potential difference?
Reverse the direction of movement of the wire
Reverse the polarity of the magnet
How do you increase the induced potential difference?
Increase the speed of movement
Increase the strength of the magnetic field
Increase the number of turns on the coil
Describe a transformer?
Two coils of insulated wire (one primary and one secondary) wound onto an iron core which produces an alternating magnetic field when a current passes through it which continually expands and collapses
What happens to the alternating magnetic field lines in a transformer?
They pass through the secondary coil and induce an alternating potential difference across the ends. If it is part of a complete circuit then an alternating current is produced
Why are the coils of wire insulated in a transformer?
So the current does not short across either the iron core or adjacent turns of wire
What’s the difference between a step up and step down transformer?
Step up makes the potential difference across the secondary coil greater than that of the primary because it’s secondary has more turns. Whereas a step down makes the potential difference greater across the primary because it has more turns
What’s a switch mode transformer?
With a ferrite core, it operates at a higher frequency, it is lighter and smaller and uses very little power when decides are not connected to it
What and why does the national grid use transformers?
They use them to step up the potential difference from power stations because the higher the potential difference, the less energy wasted
They use them to step down the potential difference so it is safe for consumers
Examples of when physics is used in hospitals?
Blood pressure measuring
ECG recordings
Endoscopes
Scanners
