define//magnetic fields Flashcards
Explain how magnetic fields occur
Describe and explain what happens when current passes through a wire in a magnetic field
A current-carrying conductor produces its own magnetic field
When interacting with an external magnetic field, it will experience a force
Conditions for Fleming’s left hand rule
When the force, the magnetic field and the current are all mutually perpendicular to each other, the directions of each can be interpreted by Fleming’s left-hand rule
The direction of current is conventional current (positive to negative)
Define magnetic flux density
The magnetic flux density B is defined as the force acting per unit current per unit length on a current-carrying conductor placed perpendicular to the magnetic field
Define Tesla
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
Describe what happens when a charged particle moves through a magnetic field
When an electron enters a magnetic field from the left, and if the magnetic field is directed into the page, then the force on it will be directed upwards
The force due to the magnetic field is always perpendicular to the velocity of the electron
Note: this is equivalent to circular motion
Describe the trajectory of a charged particle moving parallel to a uniform magnetic field
if a particle travels parallel to a magnetic field, it will not experience a magnetic force
Describe cyclotrons and explain how they and similar particle accelerators use the force that acts on a charged particle moving perpendicular to a magnetic field
radius of a particle moving in circular motion in a gravitational field
F=mv^2/r (circular motion)
F=Bqv hence
mv/r=Bq
r=mv/Bq
Define magnetic flux
The magnetic flux is defined as the product of the magnetic flux density and the cross-sectional area perpendicular to the direction of the magnetic flux density
The magnetic flux is maximum when the magnetic field lines and the area they are travelling through are perpendicular
(it is the number of magnetic field lines through a given area)
Define flux linkage
The flux linkage is defined as the product of the magnetic flux and the number of turns of the coil
when the coil is rotating
maximum BA when cos theta=1
minimum when theta=90 as magnetic field lines are parallel to the plane of the area
State Faraday’s laws in terms of both a conductor moving relative to a magnetic field and in terms of a conductor in a changing magnetic field
Faraday’s Law links the rate of change of flux linkage with e.m.f
It is defined as:
the magnitude of the induced e.m.f is directly proportional to the rate of change in magnetic flux linkage
Define electromagnetic induction and explain it
electromagnetic induction is defined as the process in which an e.m.f is induced in a closed circuit due to changes in magnetic flux
Electromagnetic induction is a phenomenon which occurs when an e.m.f is induced when a conductor moves through a magnetic field
When the conductor cuts through the 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
State Lenz’s law
The induced e.m.f acts in such a direction to produce effects that oppose the change causing it
factors affecting emf induced by moving coil
Factors that will increase the induced e.m.f are:
Moving the magnet faster through the coil
Adding more turns to the coil
Increasing the strength of the bar magnet
