Chapter 18 - Motors, Generators, Transformers Flashcards
Which way do the magnetic field lines curve on a magnet?
From the north pole to the South Pole
What is true about a uniform field?
The lines of a magnetic field are parallel to each other
What does increasing the current do to the magnetic field?
Makes it stronger
What does reversing the current do to the magnetic field?
Reverses the magnetic field lines
What is an electromagnet made up of?
A coil of insulated wire wrapped around an iron core
When may electromagnets be used?
Scrapyard cranes, circuit breakers, electric bells, relays
In Fleming’s left hand rule what do the thumb, first and second finger represent?
Thumb - Thrust/movement
First - Field
Second - Current direction
How can you increase the force in the motor effect?
Current, coils, core
When is the force 0 in the motor effect?
If the wire is parallel to the magnetic field
When is the force at right angles in the motor effect?
When the wire and magnetic field are parallel
Describe the generator effect
Inducing a potential difference using a magnetic field
When is a potential difference induced in the generator effect?
When a wire cuts the lines of a magnetic field
How can you increase the potential difference induced in the generator effect?
Make the wire cut the magnetic field lines quicker
What is a simple generator made up of?
A coil that spins in a uniform magnetic field
When is the induced P.D of an AC generator at its peak?
When the sides of the coil cut directly across the magnetic field lines
When is the induced P.D of an AC generator at zero?
When the sides of the coil move parallel to the field lines
What does a DC generator have instead of slip rings?
Split ring commutator
Why does a transformer only work on AC?
Because a changing magnetic field is necessary to induce an AC in the secondary coil
What does a transformer contain?
Coils and an iron core
What does a switch mode transformer contain?
A ferrite core
What are the benefits of using a switch mode transformer over a regular transformer?
Lighter and smaller as well as operating at a higher frequency (50kHz-200kHz)
Why would you use a transformer?
To increase/decrease the potential difference
What is true about the turns of a primary and secondary on a step down transformer?
More turns on the primary than secondary
What is true about the turns of a primary and secondary on a step up transformer?
More coils on the secondary than primary
How efficient are transformers?
Very - nearly 100%
