Magnetism and Electromagnetism Flashcards
What is magnetism?
A measurable characteristic of a moving electrical charge.
There are three classifications of magnetic materials; what are these in order of magnetic ability?
- Ferromagnetic materials (most magnetic - Iron)
- Paramagnetic materials (sometimes magnetic - Aluminum)
- Diamagnetic materials (never magnetic - Carbon)
What is the difference between a permanent and temporary magnet?
A temporary magnet loses it’s magnetism quickly after it’s magnetising force is lost.
A permanent magnet will lose it’s magnetism after a much longer time.
What is magnetic flux?
The lines of force of a magnetic field are collectively known as flux.
Symbol is Φ.
What is flux density?
Flux density is the quantity of flux lines through a cross sectional area.
Flux density determines the strength of the magnetic field.
Symbol is ß.
What is permeability?
The ease at which flux magnetizes a material.
Symbol is µ.
What are the seven characteristics of magnetic flux?
Lines:
- Form closed loops
- Are directional
- Do not intersect
- Try to shorten themselves
- Repel each other
- Seek the path of least reluctance
- Can enter any material.
What is reluctance?
The opposition of a material to accepting a magnetic path through itself.
Symbol is Rm.
What is residual magnetism?
Leftover aligned magnetic domains after a magnetising force is removed.
What is retentivity?
A material’s ability to retain magnetism.
What is saturation?
When all magnetic domains in a material are aligned.
Any further application of a magnetising force will only produce waste.
Which material is more reluctant, air or soft iron?
Air is.
Magnetic flux flows from “_____”, outside of a magnet.
North pole to south pole.
How would one use a left hand rule for coils?
- Thumb points to north pole.
- Fingers point in direction of electron flow.
How would one use a left hand rule for conductors?
- Thumb points in the direction of electron flow.
- Fingers curl in the same way as the magnetic field produced (north to south).
What are three factors affecting the strength of an electromagnet?
- The amount of current in the coil.
- The number of turns in the coil.
- The type of core used.
What are the two most common types of Iron losses?
How are they reduced?
- Hysteresis losses: The flip flopping of magnetic domains in the core due to ac current, lost as friction heat.
- Reduced with a silicon steel alloy core.
- Eddy current losses: Heat losses due to induced circulating current in the core.
- Reduced by lamination of the core.
What is Lenz’s law of induction?
Induced voltage will cause a current to flow and it’s magnetic effect will oppose the change which produced it.
What is inductance symbolized by, and what is it measured in?
Symbolized by L.
Measured in Henrys (H).
What is Flemming’s left hand rule?
- Thumb points in the direction of conductor motion.
- Firefinger points in the direction of magnetic field from north to south.
- Middle finger points in the direction of electron flow. (always perpendicular to forefinger)
What is Faraday’s law of induction?
A voltage will be produced across a conductor which cuts across magnetic flux.
This voltage is proportional to the rate of cutting flux.
1 Volt is produced by cutting across 100 million lines of force in 1 second.
What is the most noticeable effect of inductance?
Current takes longer to establish and dissipate.
What is mutual induction?
When current through one coil magnetically induces a voltage on a coil mounted on the same core but not electrically connected.
When both electrons in a pair of an atom are spinning in opposite directions, the net value of magnetism is…?
0.
Which materials are added to high carbon steel to make permanent magnets?
- Cobalt
- Molybdenum
- Chrome-tungsten
- Alnico-5 (most common).
