Magnetic field Flashcards
What three things create magnetic fields around them?
Permanent magnets, current carrying conductors(electromagnets) and moving charged particles.
How can we visualise the magnetic field?
we can visualise the magnetic field by sketching magnetic field lines
which direction does a magnet point to?
from north to south
How can you work out the direction of magnetic field?
Fleming’s left hand rule
what three things can be worked out from the fleming’s left hand rule?
the direction of force,F,
the direction of magnetic field,B,
the direction of electric current,I
can you draw the magnetic field of a bar magnet?
can you draw the magnetic field of two north pole bar magnets?
can you draw the magnetic field of a north pole magenet and a south pole magnet?
what quantity would magnetic fields be
vector
what kind of loop do magnetic field lines form?
close loops
would the field lines cross each other?
No, the field lines never cross each other
________ are often used for electromagnets and why?
iron cores because they concentrate the magnetic field lines, and create a stronger magnetic field
How can we know how strong a magnetic field is?
it can be visualised by the dendity of the field lines - the closer they are the stronger the field
what is the other name and unit for magnetic field lines?
magnetic flux, Φm, nd is measured in webers, Wb
what is the other name and unit for the strength of the magnetic field?
magnetic flux density, B
Tesla, T
How do we calculate magnetic flux density? (equation)
B = Φm/A
what do wires create when currents flow through it?
magnetic field
How do we work out the direction of the field?
using right hand grip rule
what is thumb represent in right hand grip rule?
the direction of the current
can you draw the magnetic field when a current flows through a wire from (bottom is negative)
What three things create magnetic fields around them?
Permanent magnets, current carrying conductors(electromagnets) and moving charged particles.
What is a field?
It’s a region in which a force act
when _____ flow in a ______, ________is induced around the ________.
when current flows in a wire, a magnetic field is induced around the wire.
how do you work out the direction of magnetic field around a current-carrying wire?
right-hand rule.
what is the thumb represent in right hand rule?
the direction of current
what are the curled fingers represent in right-hand rule?
the direction of magnetic field
what is a solenoid?
a thing with a lot of coils
can u draw the magnetic field created by a current-carrying wire in a coil?
…
can you draw the magnetic field created by a current-carrying wire in a lots of coils.
…. kind of like a bar magnetic
what is motor effect?
the force is perpendicular to the wire and to the lines of force.
can you draw out the motor effect?
what does the magnitude of the force depends on? (5)
the current, the strength of the magnetic field, the length of the wire and the angle between the lines of force and the field and the current direction
what is the eqaution for force?
F = BIL
how does a motor work?
http://www.animations.physics.unsw.edu.au/jw/electricmotors.html
how do you work out the velocity of a charged particle in a magnetic field?
V = F/BQ
how do we find out the force which is acting on a charged particle in a magnetic field which is a x angle to the the lines of force?
F = Bqv sin x
How can you make a current carring wire ina magnetic field vibrate? can you use left hand rule to find the direction of the force?
by passing an alternating current. (see p.73)
what is magnetic flux density?
the force on one metre of wire carrying a current of one amp at right angle to the magnetic field
what is the definition of one tesla?
1 tesla = 1 Wb/m2
how do you find out the force on a current carrying wire?
F = Bil
what would a charged particle experience in a magnetic field?
a force
why are charged particles in a magnetic field deflected in a circular path?
the force is always perpendicular to the current. that’s the condition for circular motion.
what is a particle’s acceleration?
a = v2/r
how do you derive the formula for radius of the circular path?
F = mv2/r = BQv
mv2/r = BQv
r = mv/BQ
how do you find out the frequency of rotation?
f = v/2(3.14)r
f = BQ/2(3.14)m
what does the formular of frequency tell you?
the frequency of rotation of a charged particle in a magnetic field is independant of its velocity. the time it takes a particle to complete a full circle depends only on the magnetic flux density and its mass and charge
what would happen if you increase a particle’s velocity?
it will make it follow a circular path with a larger radius, but it will take the same amount of time to complete it.
If a ___________ moves through a _________ its _______ will experience a _______.
if a conducting rod moved through a magnetic field its electrons will experience a force.
how to induce an emf?
when there is realtive motion between a conductor and a magnet
if a conducting rod moves through a ____________ its electrons will experience a force, which means that they _______________ at ______. this induces an _______ across the ends of the rod.
magnetic field, accumulate, one end, emf
flux linking
when an emf. is induced by changing the magnitude or direction of the magnetic flux (eg. by using an alternarting current)
magnetic flux
magnetic flux density, B, is a measure of the strength of the magbetic field per unit area.
Wb = BA
flux linkage
when a wire coil is moved in a magnetic field, an e.m.f. is induced across the coil.
= N Φ = BAN
Φ = ?
BAcosx
BA
what is the angle which we consider in flux linkage
angle between the normal to the plane of the coil and the magnetic field
faraday’s law
induced emf is directly proportional to the rate of change of flux linkage
magnitude of induced emf = rate of change of flux linkage
= N change of Φ / change of t
Lenz’s law
the induced e.m.f. is always in such a direction as to oppose the change that caused it
the idea that an induced emf will oppose the change that caused it agrees with the principle of the conservation of energy
NΦ = ?
BANcoswt
theta = wt
