Magnetism Flashcards
true or false; any breaks in a series circuit ceases the current to flow
true
what is the equation for cost of electricity?
Cost = Power (kW) * time (hrs)* cost (cents/ kWh)
Define magnetism
fundamental property of matter
- physical property of matter that causes certain materials to experience a force when near other magnets or magnetic fields
- magnetic materials : Fe, Ni, Co, neodymium
What is a permanent magnet
object that displays persistent magnetism
what are the two magnetic regions
south and north pole
true or false; magnetic monopoles exist
false
- there is no such thing
why don’t magnetic monopoles exist
when a magnet is cut in half; poles will re-establish themselves
when do magnets experience a force
when around other magnets
what are the fundamental laws of magnetism
like poles repel
opposite poles attract
What is a magnetic force
mediated by a magnetic field
- surrounds a magnet (just like E-field surrounds a charge)
what is the symbol for magnetic field
B
true or false; magnetic field has a magnitude and direction
true
Which direction do the arrows (field lines) go
north to south pole
What are the units for magnetic fields
Tesla (T) = 10 000 Gauss (G)
true or false; north pole is pushed along the field lines
true
true or false; south pole is pushed along the field lines
false; south pole is pushed against the field lines
true or false; a magnet put in an external magnetic field will attempt to align itself parallel to the field lines
true
The Earth is like a big bar magnet. The north pole of a compass needle points towards North (North Canada to be precise). Where is the magnetic south pole of the Earth?
North Canada
- because north of a compass is attracted to south pole of the Earth
what causes an electric charge
is the lack or excess of elementary electric charges (electrons)
What did Oersted show?
that a current flowing through a wire can deflect a compass needle
What was Oersted’s demonstration
he placed a magnetic needle beneath a current carrying wire
true or false; an electric current produces a magnetic field
true
What is current
the flow of electric charge
what is the source of all magnetism
the movement of electric charge
what are the 2 quantum mechanical contributions that describes an electrons movement
- electrons: spin angular momentum
- orbitals: orbital angular momentum
what are electrons
fermions
describe the characteristics of an electrons
- no two electrons have the exact same set of characteristics
- only two electrons can fit inside a single box, and they must have opposite magnetic moments
- if two electrons have the opposite magnetic moments they cancel
true or false; unpaired electrons are required for a material to be magnetic
true
true or false; if the magnetic moments of the atoms point to random directions they cancel
true
What is the effect of an external magnetic field to randomly oriented atoms
they align parallel
- but when the field is turned off, the random orientation returns
What is a ferromagnet
they want to align magnetic moments parallel
define magnetic domain
region where the magnetic moments of atoms are aligned parallel
If a weak external magnetic field is turned off, how does this affect the conductor?
thermal motion aligns the domains randomly after the field turned off
if a strong external magnetic field is turned off, how does this affect the conductor?
domains stay aligned after the field is removed
- the material then becomes a permanent magnet
What is another method to make a permanent magnet?
stroke a piece of iron with magnet to align all the domains
Why does dropping or heating the magnet cause the domains to weaken?
domains can jostle out of alignment
what is an electromagnet?
type of magnet in which the magnetic field is produced by the flow of electric current
- stopping current stops magnetism
What is a current loop
produces a magnetic field concentrated in the center of the loop, pointing away or towards the screen
true or false; a strong magnetic field can be generated by winding a wire into a coil
true, called a solenoid
when does a solenoid act as a magnet
only when current is flowing
true or false; stationary charge in a static magnetic field experiences no net force
true
- will not be moved to any direction
- align along the magnetic field
true or false; moving charge does not experience a force, in the magnetic field
false; it does experience a force
- force is perpendicular to the magnetic field and to the direction of charge motion
What does F stand for?
Force on a charge moving perpendicular to the magnetic field
what is equation for finding the force on a charge moving perpendicular to to the magnetic field?
F= qv B
q: charge
v: speed
B: magnetic field magnitude (T)
true or false; if there is no current there is no movement of charge and hence no force on the wire
true
what does current flowing mean
it means that charges experience the Lorentz force
what is the equation for Lorentz force
F= I* L* B
I: current
L: length (m)
B: magnitude of magnetic field
What is electromagnetic induction
changing a magnetic field can give rise to an electric current in a conducting wire
(discovered by Micheal Faraday and Joseph Henry independently in 1831)
What can the changing magnetic field be realized by
a moving magnet
- or a moving conductor in a static magnetic field
what happens eg.a moving magnet, is realized by a changing magnetic field
voltage is caused or induced across the conductor
- which results in the flow of current
- even without any battery connected
what does Faraday’s law state?
-the greater the number of loops of wire that move in a magnetic field, the greater the induced voltage
true or false; you can create electrical energy from nothing by simply moving a magnet
false
it is not possible
what does Lentz law state
- The induced voltage gives rise to a current. Currents always give rise to a magnetic field
- the poles of the induced magnetic field are always such that they oppose the movement of the magnet
- therefore there is a repulsive force one must overcome to move the magnet through the coil
- this means mechanical work is required
true or false; electromagnetic induction allows mechanical energy to be transformed into electrical energy
true
What is a generator
a simple apparatus in which coil is rotated in a static magnetic field
mechanical energy is converted into electrical energy
What happens when the string of an electrical guitar is plucked?
its vibration will perturb the magnetic field of the magnet. This induces a current in a coil on the pickup. The electrical signal is transmitted to an amplifier and sent to the speakers
