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)
What do the components of the magnetic flux equation mean
Magnetic flux linkage def
The product of the magnetic flux and the number of turns of the coil
What do the components of the magnetic flux linkage equation mean
What is magnetic flux linkage measured in
Weber turns (Wb turns)
What is the symbol for magnetic flux linkage
ΦN
What do the components of the magnetic flux linkage equation mean (When the magnet field lines are not completely perpendicular to the area A)
When is an emf induced in a circuit
When there is:
- A changing magnetic flux density B
- A changing cross-sectional area A
- A change in angle θ
What is electromagnetic induction
when an e.m.f is induced when a conductor moves through a magnetic field
What happens when a conductor cuts through magnetic field lines
- This causes a change in magnetic flux (ΔΦ)
- Which causes work to be done
- This work is then transformed into electrical energy
Electromagnetic induction def
The process in which an e.m.f is induced in a closed circuit due to changes in magnetic flux
When may electromagnetic induction occur
When:
- A conductor cuts through a magnetic field
- The direction of a magnetic field through a coil changes
What is electromagnetic induction used for
- Electrical generators which convert mechanical energy to electrical energy
- Transformers which are used in electrical power transmission
What factors increase an induced e.m.f when a bar magnet is moved through a coil connected to a voltmeter to induce an e.m.f
- Moving the magnet faster through the coil
- Adding more turns to the coil
- Increasing the strength of the bar magnet
What factors increase an induced e.m.f when a wire is moved between two magnets connected to a voltmeter to induce an e.m.f
- Increasing the length of the wire
- Moving the wire between the magnets faster
- Increasing the strength of the magnets
What does Faraday’s law state
The magnitude of the induced e.m.f is directly proportional to the rate of change in magnetic flux linkage
What does Lenz’s law state
The direction of the induced emf is such that it will oppose the change of flux producing it
Describe the experimental evidence for Lenz’s law
What do the components of Faraday’s law equation mean
What does Faraday’s law equation demonstrate
that the gradient of a magnetic flux against time graph is the e.m.f
What is the equation that combines Faraday and Lenz’s laws AND what does it demonstrate
Draw a diagram which shows how a straight conducting rod moving through a magnetic field will have an e.m.f induced in it
Derive the equation for the induced e.m.f in a conductor as it moves through the magnetic field
When is induced emf at a maximum/ minimum
- Maximum when θ = 90o. The magnetic field lines are parallel to the plane of the area (or the normal to the area is perpendicular to the field lines)
- 0 when θ = 0o. The magnetic fields lines are perpendicular to the plane of the area (or the normal to the area is parallel to the field lines)
Draw a graph of the magnetic flux linkage and e.m.f induced as a coil rotates in a magnetic field
Describe the derivation and components of the ‘emf induced in a rotating coil’ equation
Derive the frequency equation
