magnetic fields and induction Flashcards
(49 cards)
how are magnetic fields produced
by permanent magnets and around conductors carrying a current
definition of magnetic flux density
the force per unit length per unit current carrying conductor at right angles to the magnetic field lines ( B = F/IL )
what does it mean if the field lines are closer together
the field is stronger
what is 1 tesla
the magnetic flux density that produces a force of 1 newton on a wire of length 1 metre with 1 ampere of current flowing through it
what happens when a current carrying conductor is placed in a magnetic field and what can be used to find the direction of this
the conductor experiences a force that can be found using flemmings left hand rule
where is the magnetic field going if there are x’s on the page
in to the page
where is the magnetic field going if there are dots on the page
out of the page
when can we use F=BIL
when the angle between the magnetic field and the current is 90 degrees
what happens when the current is parallel to the field lines
there is no force induced
what is the catapult effect
occurs when a current is passed through two wires connected by a loose wire or bar in a magnetic field
due to flemings left hand rule, the loose wire is then catapulted horizontally away from the magnetic field
this occurs due to the magnetic forces acting on the wires and in the magnetic fields itself
how is a magnetic field formed around a current carrying wire and what do we use to find the direction of the field lines
they form concentric circles around the wire and the direction can be found using the right hand grip rule
what happens when two wires carry current in opposite directions
the net effect of their magnetic fields is added together in the space between the two wires
what happens when two wires carry current in the same direction
the net effect is to cancel out the magnetic field the space between the wires
how to find the direction of current in a solenoid
anticlockwise = north
clockwise = south
what is magnetic flux measured in and what is the equation
magnetic flux = BA
measured in Wb (Weber)
what is the equation for flux linkage if it is at an angle to the normal of the coil
flux linkage = NBAcosx
equation for force on charged particles moving in a magnetic field and when is it valid
F = BQV
valid when the charge is moving perpendicular to the field lines
what happens if the particle is moving parallel to the field lines or if the particle is not moving
there is no magnetic force
equation for force on charged particles moving in a magnetic field that is not at 90 degrees
F = BQvsinx
what direction is current when there is a positive charge
the same direction as the positive charge
what path will a charged particle take in a magnetic field and what is the equation
circular path
r = mv/BQ
what happens if a particle moves through a cloud chamber
it will lose energy because it is giving energy to the molecules in the chamber so it will slow down and spiral inwards
what is a cyclotron
a particle accelerator
how does a cyclotron work
- there is an electric field and therefore a potential difference horizontally between 2 dees
- the protons accelerate when they cross the gap between the dees
- the magnetic field is perpendicular to the motion of the protons
- the protons move in circular motion when inside the dees
- when the speed of the protons increases the radius of the path increases (r = mv/BQ)
- we want the protons to speed up every time they cross the gap
- we do this by switching the direction of the electric field every time the protons undergo one half circle
- we can switch the direction of the electric field using an alternating power supply
- the frequency of the supply should equal the frequency of the circular motion of the protons
- v = rBQ/m
- time for 1 half circle =
pi r / v - f = BQ/ 2 pi m
- the frequency does not depend on the radius of the path so we can use an ac supply of constant frequency
