Ch 4 Electricity, Magnetism & Electromagnestism Flashcards
*electrostatics is:
the study of stationary electric charges
*matter has ____ and _______, matter may also have ____
mass and energy equivalence, may also have electric charge
being electrified means there is:
too few or too many electrons
*electrification can be created by:
contact, friction & induction
*unlike charges ___; like charges _____
attract; repel
the force of attraction b/w 2 unlike charges or the force of repulsion b/w 2 like charges is called ____
electrostatic force
*Coulomb’s law: the electrostatic force is directly proportional to ______ and inversely proportional to the ____
the product of the electrostatic charges; square of the distance b/w them
electrostatic force is very strong when ____ and rapidly decreases when ____
objects are close together; objects are separated
*electric charge distribution is:
uniform throughout or on the surface
*electric charge of a conductor is:
concentrated along the sharpest curvature of the surface
*the unit of electric potential is:
volt (V)
the higher the voltage the ____ the potential to do work
greater
if electric potential is applied to an object then:
electrons move along that object in an electric current or electricity
*electrodynamics is:
the study of electric charges in motion
the direction of electric current is always:
opposite that of electron flow
*a conductor is:
any substance in which electrons flow easily; metals, copper, water
*an insulator is:
any material that does not allow electron flow; glass, clay, earth like materials
semiconduction
demonstrated in 1946 by William Shockley, materials are Si silicon and Ge germanium, led to microchips and computer technology
*a semiconductor is:
any material that under come conditions acts as a conductor while under other conditions acts as an insulator
superconductivity
the property of some materials to exhibit no resistance below a critical temperature (Tc)
an electric circuit is when:
the resistance is controlled and the conductor is a closed path
*increasing electric resistance results in:
a reduced electric current
electric current is measured in ____
amperes (A)
an A is proportional to the:
number of electrons flowing in the electric circuit
1A=
1 electric charge flowing per second
electric resistance is measured in ____
ohms
*Ohm’s Law:
the voltage across a total circuit or any portion of the circuit is equal to the current times the resistance V=IR
*in a series circuit all circuit elements are:
connected in a line across the same conductor
*a parallel circuit contains elements that are:
connected at their ends rather than lying in a line across the conductor
*direct current (DC):
electrons can be made to flow one direction along the conductor
alternating current (AC)____, occurs____, is ___Hz
current where electrons oscillate back and forth, occur sinusoidally requiring 1/60 s, 60Hz current
DC is represented by:
a horizontal line
AC is represented by:
a sine curve, electrons flow positively first, then negatively
*any charged particle in motion creates:
a magnetic field
*the lines of a magnetic field are always:
closed loops
lines of a magnetic field are _____ or _____ and always have a ___ and a ____
bipolar or dipolar; north and a south pole
a magnetic dipole is:
the small magnet created by the electron orbit
the accumulation of many atomic magnets with their dipoles aligned creates a:
magnetic domain
*magnetic permeability is:
the ability of a material to attract the lines of magnetic field intensity
3 principle types of magnets:
naturally occurring, artificially induced permanent magnets & electromagnets
*magnets are classified according to:
the origin of their magnetic property
electromagnets consist of:
wire wrapped around an iron core, when electric current flows through the wire a magnetic field is created
*all matter can be classified according to:
the manner in which it interacts with an external magnetic field
nonmagnetic
unaffected by a magnetic field, wood, glass
diamagnetic
weakly repelled by both poles of the magnetic field, not attracted to a magnet, water, plastic
paramagnetic
weakly attracted to both poles of a magnetic field, slightly attracted to a magnet, gadolinium, contrast agents
ferromagnetic
can be permanently magnetized by exposure to a magnetic field, strongly attracted to a magnet, iron, nickel, cobalt
like magnetic poles ____, unlike magnetic poles _____
repel, attract
some materials can be made magnetic by:
induction
imaginary magnetic fields are called _______, their density is ____
magnetic lines of induction, proportional to he intensity of the magnetic field
*ferromagnetic objects can be made into magnets by:
induction
*the magnetic force is proportional to the:
product of the magnetic pole strengths divided by the square of the distance between them
*the SI unit of magnet field strength is the ___; an older unit is the ______; __T=______G
tesla; gauss; 1T=10,000G
*electric potential is measured in units of ___
Joule per coulomb, or volt
*any charge in motion:
induces a magnetic field
a coil of wire is called a ____
solenoid
*an electromagnet is:
a current carrying coil of wire wrapped around an iron core, which intensifies the induced magnetic field
an ammeter is:
a current measuring device
*electromagnetic induction:
an electric current is induced in a circuit if some part of that circuit is in a changing magnetic field
*varying magnetic field intensity:
induces an electric current
*an induction motor:
powers the rotating anode os an x-ray tube
*a transformer:
changes the intensity of alternating voltage and current
a transformer will operate only with:
a changing electric current (AC)
step-up transformer:
has a turns ratio of greater than 1 b/c the voltage is increased from primary to secondary
step-down transformer:
has a turns ratio of less than 1
*an autotransformer has:
one winding and varies both voltage and current
current and electron flow are always:
opposite
the primary function of an x-ray imaging system is to:
convert electric energy into electromagnetic energy
in induction only ____ charges move
negative
in a transformer if the voltage goes up the current goes ___
down
examples of a small resistance:
a large diameter or a small distance
in a diode electrons flow:
in one direction
superconductors (do/dont) follow ohm’s law?
DON’T
electric and magnetic field lines are always _____
perpendicular
a photons frequency, wavelength & energy can _____, but a photon will always travel _____
vary, at the speed of light
a motor is ____ energy
mechanical
a generator is ____ energy
electric
the ground is where everything _____, the earth has ____ charges
neutralizes, negative
2 coils is _____; 1 coil is _____
mutual induction; self induction
in the domain magnets run:
south to north
the magnetic field runs:
north to south
the domain is ___ the magnet
within
