6.2 Magnetic Flux Density Flashcards
When is a force exerted in a magnetic field?
When magnetic fields interact.
Why do lines that are closer mean the force that will be exerted will be greater?
As the magnetic field strength would be greater due to lines being closer, meaning the force will also be greater.
What is the magnetic flux density?
the force on 1m of wire carrying current of 1A at right angles to magnetic field.
What happens if current supplied is parallel to magnetic field lines?
No force is exerted.
What happens if current supplied is perpendicular to magnetic field lines?
Max force is exerted/
What do we have to do when current supplied is e.g. at an angle of 30 to horizontal?
We have to use trigonometry to work out the force acting in the perpendicular component to magnetic field.
What do we use to work out force/motion , direction of current , direction of field of interacting magnetic components?
Flemings Left Hand Rule
What does the thumb represent in the flemings left hand rule?
The motion/direction of force
What does the first finger represent in flemings left hand rule?
Direction of the magnetic field.
What does the second finger represent in flemings left hand rule?
The direction of conventional current?
What is the direction of current when electrons are the charge carriers?
Opposite to the direction shown by the second finger in fleming’s left hand rule.
Is magnetic flux density a vector or a scalar?
vector
what is the unit of magnetic flux density
T - tesla
or
NA^-1m^-1
What happens when a current carrying wire is placed within another magnetic field. How do we work out the directions?
It will experience a force. Using flemings left hand rule.
What does the force exerted on magnetic materials when their magnetic fields interact is proportional to?
force is proportional to current x length of wire
What is the equation for force? bil
What does each letter represent?
F = bil F = force (N) b = magnetic flux density I = current(A) L = length (m)
In the F = BIL there is usually a suffix under the B , what does it represent?
That the wire carrying the current must be perpendicular to the direction of the magnetic field.
When taking angles into account, what does the f = bil equation become?
F = BIL sinx
Except straight conductors what else can experiance a force in the magnetic field?
Charged particles that are moving
What is the equation for force of a charged moving particle in magnetic field? What does each symbol represent?
F = BQV f = force b = magnetic flux density Q = charge v = velocity
When taking angles into consideration what does f = bqv become?
F = BQVsinx
Since the magnetic field is always perpendicular to direction of travel for a charged particle what condition do we get from this?
Circular motion
Why does circular motion happen?
The velocity of the particle keeps changing (accelerating) as it is attracted to the centre where magnetic field is. So the force will also act towards the centre.
What equation can we use to work out the distance from centre that a charged particle is orbiting.
mv/BQsinx = r
Why does a charged particle follow a circular path.
Since the magnetic field is always at 90 degrees to direction of travel, so that it will be attarcted towards middle, constantly changing acceleration.
Describe the practical for finding force acting on the wire in a magnetic field.
A U-Magnet is placed on scale. The value is zeroed. The wire is put within the poles of the magnet and current is switched on.
What happens when the current is switched on in this practical?
The values of the scale should change (and be noted)
Why does this happen?
As the wire is fixed in place, the force exerted on it is equal to the force exerted on the magnet (newtons 3rd law) and so the magnet should apply more pressure or less to the scale.
How do we calculate the force in this practical?
The value of the scale (change in mass of magnet)x 9.81
What would a graph of F/I give us as gradient? What do we need to do to get B on its own.
BL, so we need to divide by length of wire in the poles to get magnetic field
What is the length of the wire in this practical?
Only the length placed within the magnetic field of the U magnet.
What is one safety precaution in this experiment?
The power supply should be switched off between readings so that the wire doesn’t get hot.
What is flux linkage?
amount of magnetic flux interacting with a coil of wire
