Magnetic Fields Flashcards
What does a current-carrying conductor produce
a magnetic field
When interacting with an external magnetic field, it will experience a force
When will a current-carrying conductor experience the maximum magnetic force
if the current through it is perpendicular to the direction of the magnetic field lines
It experiences no force if it is parallel to magnetic field lines
What is the strength of the magnetic field known as, and what is its unit
the magnetic flux density, B
measured in Tesla (T)
Describe the components of the force-flux density equation
What does the force-flux density equation show
the greater the current or the magnetic field strength, the greater the force on the conductor
What is Flemings’s left hand rule
What are the symbols for a magnetic field which goes into or out of the page
Describe how moving charges may curve in direction
For example, when a positively charged particle enters a magnetic field into the page from left to right:
-Using Fleming’s left-hand rule, the first finger points into the page and the second finger (current) points to the right
- This means the force is upwards
- The particle is then pulled in the direction of this force (upwards). This means the direction of the current also changes direction slightly (slanting upwards)
- This means the force will also change direction since it still needs to keep perpendicular to the current and the field
- Therefore, the moving charges will follow a circular trajectory
Magnetic flux density def
The force acting per unit current per unit length on a current-carrying conductor placed perpendicular to the magnetic field
Measured in Tesla
unit of a Tesla def
A wire carrying a current of 1A normal to a magnetic field of flux density of 1 T with force per unit length of the conductor of 1 N m-1
how can a particle experience no magnetic force
when it travels parallel to a magnetic field
What does the force on a current carrying wire depend on
- Strength of uniform magnetic field
- Size of current
- Length of wire in the field
For a particle in a magnetic field, travelling in a circular path, what is the centripetal force
The magnetic force
Draw a diagram of the forces acting on a particle which moves in a circular path
What are cyclotrons
a type of particle accelerator that accelerates charged particles (eg. protons) from their centre along a spiral path
What kind of medical research are cyclotrons used for
Producing medical isotopes (tracers)
Creating high-energy beams of radiation for radiotherapy
Draw and label a diagram of a cyclotron
Describe the process of accelerating a particle in a cyclotron
- A source of charged particles is placed at the centre of the cyclotron and they are fired into one of the electrodes
- The magnetic field in the electrode makes them follow a semi-circular path, since it is perpendicular to their motion until they eventually leave the electrode
- The potential difference applied between the electrode accelerates the particles across the gap to the next electrode (since there is an electric field in the gap)
- Since the speed of the particles is now higher, they will follow a circular path with a larger radius (since r ∝ v) before leaving the electrode again
- The potential difference is then reversed so the particles accelerate towards the opposite electrode
- This process is repeated as the particles spiral outwards and eventually have a speed large enough to exit the cyclotron
- The alternating potential difference is needed to accelerate the particles across the gap between opposite electrodes
- Otherwise, the particles will only accelerate in one direction
Derive the equation for the radius of the path of a particle travelling in a magnetic field
What is electromagnetic induction and give examples
- when an e.m.f is induced in a closed circuit conductor due to it moving through a magnetic field
- This happens when a conductor cuts through magnetic field lines
- The amount of e.m.f induced is determined by the magnetic flux
Examples are a flat coil or a solenoid
magnetic flux definition
The product of the magnetic flux density and the cross-sectional area perpendicular to the direction of the magnetic flux density
(the total magnetic field that passes through a given area)
When is magnetic flux at a maximum/minimum
- It is a maximum when the magnetic field lines are perpendicular to the plane of the area
- It is 0 when the magnetic field lines are parallel to the plane of the area
Draw a diagram of maximum magnetic flux and minimum magnetic flux
What is the unit of magnetic flux
Webers (Wb)
