past paper notes- magnetism Flashcards
Explain why a constant voltage VH is developed between the faces you have named in (i)? /4
- charge carriers moving normal to the magnetic field
- charge carriers experience a force normal to I
- build up of charges results in a potential difference across a slice
- VH becomes constant when FB=FE
Explain the use of a uniform magnetic field and uniform electric field for the selection of the velocity of charged particles. /4
- electric and magnetic fields are normal to each other
- velocity of particle normal to both fields
- forces on particle due to fields are in opposite directions
- forces are equal for particles at particular speeds
State what is represented by the symbol n? /1
number density of free electron
In some semiconducting materials, electrons are mainly responsible for conduction.
in other semiconducting materials, holes are mainly responsible for conduction.
suggest and explain the differences, if any, that conduction by electrons or by holes will have on the hall voltage. /3
- magnetic field would deflect holes and electrons in same direction
- because electrons are -ve and holes are +ve
- so VH has opposite sign
explain why electrons follow a circular path when inside the region of the magnetic field? /3
force is perpendicular to velocity always
magnetic force provides centripetal force
magnitude of force is constant
state the measurements needed in order to determine the charge to mass ratio e/me of an electron. /2
magnetic flux density
accelerating pd
radius of path
Explain how a uniform magnetic field and a uniform electric field may be used as a velocity selector for charged particles? /3
electric and magnetic fields are at right angles to each other
particle enters field normal to the both fields
no deviation for particles with selected velocity
State two conditions that must be satisfied for a copper wire, places in a magnetic field, to experience a magnetic force. /2
1) there must be current in wire
2) wire must be at non zero angle in magnetic field
Two long parallel current-carrying wires are placed near to each other in a vacuum.
Explain why these wires exert a magnetic force on each other. /3
currents in wire create magnetic field around each other
each wire sits in the magnetic field created by other
wire is perpendicular to magnetic field so experiences a magnetic force
A Hall probe is placed in a magnetic field. The Hall voltage is zero. The Hall probe is rotated
to a new position in the magnetic field. The Hall voltage is now maximum.
Explain these observations.
it is zero when the probe is parallel to the magnetic field lines
it is maximum when the probe is perpendicular to the magnetic field lines
