Chapter 6 - Magnetism & Electrostatics Flashcards
Who discovered that all moving electrical charges develop magnetic fields around them, when, and how?
Hans Christian Oersted
1819
magnetic compass needle was disrupted by an electrical current
What is magnetic moment?
the orientation of the magnetic field in a charged particle (proton or electron) as determined by the direction of its spin (clockwise spin, North pole faces up - counterclockwise spin, North faces down)
What is a magnetic dipole?
an entire atom that has a magnetic field due to having an odd number of electrons - one electron’s spin is not cancelIed out
What are magnetic domains?
small regions of aligned atoms in a substance which has magnetic potential, but is not magnetic as a whole
What does it mean to be ferromagnetic?
This is a material that can be easily magnetized (iron, nickel, etc.) by placing it within an external magnetic field. This causes its magnetic domains to all line up in the same direction.
What is a lodestone?
A ferromagnetic rock that behaves naturally as a weak magnet because its magnetic domains have aligned with the earth’s magnetic field.
What is magnetic permeability?
the ease with which a material can be penetrated by an external magnetic field (and thus be magnetized)
What is magnetic retentivity?
ability of the material to retain magnetism over time
How are magnetic permeability and retentivity related?
Usually high permeability = low retentivity
& vice versa
What does it mean to be paramagnetic?
material that is only slightly attracted to strong magnets
What does it mean to be diamagnetic?
material that is repelled away from magnets
What are the 2 basic laws of magnetic behavior?
- like poles repel, opposite poles attract
- Gauss’ Law
What is Gauss’ Law (description & formula)?
strength/intensity of a magnetic field is proportional to the product of pole strengths & inversely proportional to the square of the distance between them
F = k((P1)(P2) / D^2)
F = force of attraction or repulsion
P = strength of poles from 2 different magnets
D = distance between poles
k = conversion factor (usually from Gauss to newtons)
What is the conversion between Gauss & Tesla?
1 Tesla = 10,000 Gauss
What is the unit for electrical charge & What is its value in terms of electrons?
1 Coulomb = 6.3×10^18 electrons
(6 BILLION BILLION)
What are the 5 laws of electrostatics?
- like charges repel - opposite charges attract
- in solid objects, only negative charges can move
- in solid objects, electrical charges exist only on the surface
- in solid objects, electrical charge will concentrate at the greatest curvature of the surface
- Coulomb’s Law
What does Coulomb’s Law state?
the amount of force generated by electrical repulsion /attraction is proportional to the product of the two charges and inversely proportional to the square of the distance between them
F = k((Q1)(Q2) / D^2)
F = force of attraction or repulsion
Q = amount of charge on each object
D = distance between objects
k = conversion factor (from Coulombs to volts or newtons)
What are the 3 ways an object can become electrified?
- friction
- contact
- induction
How is electrification by friction caused?
Two electrically neutral objects rub against one another - loosely bound electrons from one are stripped & deposited on the other. This gives one object a net positive charge and one object a net negative charge.
How is electrification by contact (conduction) caused?
A difference in electrical charge between two objects will cause electrons to flow towards the object that is more positively charged when they make contact until the charges equalize.
How is electrification by induction caused?
a charged object changes the charge in another object without making direct contact by using the forces of attraction & repulsion - usually causes polarization in the object being induced
What is electromotive force?
force created by a difference in potential (electrical pressure)
What is the unit of measure for EMF (electromotive force)?
the volt
What are the two requirements for a subatomic particle to acquire a magnetic moment?
- SPIN
- AN ELECTRICAL CHARGE
What are the four classifications of materials relative to their magnetic permeability?
- FERROMAGNETIC
- PARAMAGNETIC
- NON-MAGNETIC
- DIAMAGNETIC
Where would the earth’s magnetic field be most concentrated?
THE POLES
What are the three general types of magnets?
- NATURAL
- ARTIFICIAL
- ELECTROMAGNET
The principle reservoir for the deposit of excess electrical charge is:
THE GROUND
What are the two reasons why only electrons move in charged, solid objects?
- ATOMS ARE LOCKED IN PLACE AND CAN NOT MOVE
- PROTONS ARE LOCKED IN THE NUCLEUS, SO ONLY OUTER SHELL ELECTRONS CAN MOVE
When a charged object comes close to an uncharged object but does not touch it, what is the term for the separation of charges in the second object which results?
POLARIZATION
As x-rays ionize atoms of air in a pocket dosimeter, what happens to the electrical charge placed on the metal foil leaves of the electroscope?
THE POSITIVE CHARGE ON THE FOIL IS NEUTRALIZED BY THE NEGATIVE ELECTRONS FROM THE AIR
What does it mean to be non-magnetic?
a material that is not affected by magnets
What happens to a magnet’s poles if you break it in half?
It remains dipolar/bipolar and each will have its own N/S pole.
What is a solenoid?
A coil of wire that carries electrical current as part of an electromagnet
How does magnetic force flow along the lines of force?
outward and around from the North pole, then into the South pole
How does magnetic force flow along the lines of force?
outward and around from the North pole, then into the South pole
What are the units with which magnetic pole strength is measured?
Gauss (G)
What is electrostatics?
The study of electrical charges at rest (static electricity)
What are 3 ways to minimize static discharges?
- INSULATE electrical wires and devices
- GROUND metal structures
- Keep HUMIDITY levels high (40% & higher)
