Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
20 Cards in this Set
- Front
- Back
|
Magnetic field |
Magnetic field is a region where the magnetic force is exerted on magnetic materials |
|
|
The right hand rule |
Gives a simple way to remember the direction of the field. For a straight wire: thumb = current Fingers = lines of flux For inside a coil: thumb = lines of flux Fingers = current |
|
|
Flux lines |
The lines of flux show both the direction and strength of the magnetic field |
|
|
Fleming's LHR |
You can use the LHR to predict the direction of the force First finger = direction of flux lines Second finger = current direction Thumb = force/thrust direction |
|
|
Induction motors |
Operate by altering the magnetic field around a coil of wire that is free to move, which induces a current in the wire, causing it to rotate |
|
|
Magnetic flux |
Has the symbol phi, it represents the total number of lines of flux that link, or pass at 90 degrees through a given area. Measure in Wb |
|
|
Induced e.m.f |
E.m.f is induced where there is a change in the flux linking a conductor |
|
|
Magnetic flux density |
The stronger the magnetic field, the more densely packed the lines of flux. This is the quantity of flux passing through unit area, at each point in the field. Measure in Telsla |
|
|
Number of turns |
Each turn of the coil has flux linking it |
|
|
Conducting rod |
When moving in a electric field, electrons accumulate at one end making it negative. This is an induced voltage. Stored as electrical energy otherwise known as e.m.f |
|
|
Electromagnetic induction |
Is the production of an e.m.f across a conductor exposed over time with varying magnetic feilds |
|
|
Faraday's Law |
The induced e.m.f is directly proportional to the rate of change of flux linkage |
|
|
Lenz's Law |
The induced e.m.f is always in such a direction as to oppose the change that caused it |
|
|
Permeability |
The permeability of a material is a measure of its effect on the strength of the magnetic field |
|
|
Eddy currents |
Are currents induced in a conductor, always induced in a direction so as to oppose thr motion of the change in flux |
|
|
Alternator |
Is a generator if alternating current |
|
|
Slip rings |
Used in ac generators, they rotate with the coil and press against stationary carbon brushes. Each side of coil always makes contact with the same brush. |
|
|
Split ring commutator |
The commutator reverses thr direction of current flow around the coil every half turn, so the coil rotates continously |
|
|
Ferro magnetic |
In ferromagnetic materials these tiny atomic magnets can line up with each other to produce a strong magnet. All the donames are aligned. Half field shells. |
|
|
Angle of dip |
The lines of flux act at angle to the Earth's surface, except near the equator. This angle is called the angle of dip. It the UK it is about 70 degrees |
