Unit 4 Chapter 4 Electricity, Magnetism and Electromagnetism Flashcards
The science of stationary electric charges
electrostatics (static electricity)
the science of electric charges in motion
electrodynamics
the xray imaging system is made to do what
convert electric energy into electromagnetic energy
means of transferring electric potential energy from one position to another as in a transformer
electromagnetic induction
electric energy is supplied to the imaging system as a well controlled……
electric current
in the xray tube, some of the energy is converted to electromagnetic energy, while most is converted to …..
heat. 1% converted into xrays, 99% to heat
electric charges come in what kind of units
discrete units that are positive or negative
apart or detached from others; separate; distinct
discrete
most discussions of electric charge deal with?
negative electric charges associated with electrons
why are protons not as free to travel as electrons are
because they are bound so tightly in the nucleus
what kind of charge to electrons have?
one unit of negative charge
what kind of charge to protons have?
one unit of positive charge
protons and electrons have opposite signs(charges) but the same what?
magnitude
when an object has too many or too few electrons what does that mean
electrification
how do you CREATE electrification
by contact, friction or induction
some atoms have outer shell electrons that are loosely bound and can……
be removed easily
what happens when loosely bound electrons are removed
causes the object they were removed from to become electrified and produces static electricity
rubbing your feet on the carpet causes a buildup of electrons causing you to ……
become electrified
why does your hair stand up when you rub a balloon on your head?
the negatively charged particles are repulsed from each other
after creating static with a balloon on your hair, why wont it lay back down nicely
because the negative charged particles are trying to get away from each other
the earth is always available to accept excess electric charges…what is it called then
an electric ground
during a thunderstorm, electrons can be moved….
from cloud to cloud
how do clouds return to their normal state
lightining
lightning can occur between….
clouds of differing charges and between the clouds and the earth
coulomb (unit of electric charge)
1C=6.3 x 10^18
the electrostatic force is directly proportional to the product of the electrostatic charges and inversely proportional to the square of the distance
coulomb’s law
F=k QaQb/d^2
how is electric charge distribution?
uniform throughout or on the surface
electric charge of a conductor is concentrated
along the sharpest curvature of the surface
associated with an electric charge
electric field
what way does the field of a positively charged object point
outward
what way does the field of a negatively charged object point
inward
do uncharged particles have an electric field
no
how will the magnetic field of UNLIKE charges react to each other
the magnetic filed will pull them towards one another, the negative pulling inward and the positive pushing outward
how will the magnetic fields of LIKE charges react
they will cause objects to be physically repulsed from one another
electrostatic force is directly _______ to the product of electrostatic charges
proportional
the more charges that are present, the ______ the force will be
stronger
electrostatic force is _______proportional to the square of the distance between them
inversely
as distance increases, electrostatic force
decreases
how are electric charges distributed on the surface of copper wire
evenly
on a cattle prod, where will the charges be concentrated?
at the surface (it is a conductor and the tip is the curvature)
Think what when it comes to electric potential?
voltage
the measure of work required by and electric field to move electric charges
electric potential
the unit of electric potential
volt, also called voltage
electric charges have__________
Potential energy
electric charges can do work, when ______charges are close to each other, they can do work when they _____apart
like; fly
higher voltage means
a greater ability to do work
electric current is always opposite of ________
electron flow
what is it called when electric potential is applied to objects such as copper wire, then electrons move along the wire?
electric current, or electricity
any substance through which electrons flow easily
conductor(copper, aluminum)
any material that does not allow electron flow
insulator(Rubber, glass)
a material that under some conditions behaves as an insulator and in other conditions behaves as a conductor
semiconductor
the property of some materials to exhibit no resistance below a critical temperature
superconductivity
electrons flow alternately in one direction and then the other
ac current (alternating current)
electrons flow in one direction only
dc(direct current)
what kind of circuit has all circuit elements connected in a straight line along the same conductor
series circuit
what kind of circuit contains elements that are connected at their ends rather than lying in a line along a conductor
parallel circuit
formula for power
P=IV
path of electron flow from the generating source through the various components and back again
electric circuit
unit for current
Ampere (A)
unit for resistance
Ohms
the flow of electrons and measured in amperes
current
one ampere is equal to an electric charge of?
1C (coulomb) per second
electric potential is measured?
volts
changing the size of the wire electrons may flow through _____ the resistance of the circuit
varies
as resistance______, current_______
increases; decreases
the voltage across the total circuit or any portion of the circuit is equal to the ___
current times the resistance
V=IR and????
R=V/I and I=V/R
what is the current of an electric voltage that flows 10 amps and has a resistance of 0.5 ohms?
5 volts
two basic types of circuits are?
parallel and series
in a series circuit, all circuit elements are connected in a ___ along the same conductor
line
in a parallel circuit, elements are connected at their ___rather than lying in a line along a conductor
ends
the total resistance is equal to the ___of all resistances
sum
the current through each circuit element is the same and equal to the
total circuit current
the sum of the ____ across each circuit element is equal to the total circuit voltage
voltage
the total resistance is the __ of the sum of the reciprocals of each individual resistance
inverse
the sum of the current through each circuit element is equal to the __circuit current
total
the voltage across each circuit element is the same and is ___ to the circuit voltage
equal
Christmas lights can be wired in a
series or parallel circuit
when Christmas lights are wired in a series, one light going out——-
causes the entire circuit to go out. the circuit has been broken
when Christmas lights are wired in a parallel, one light going out
does not cause the circuit to break, and the string will continue glowing aside from the bad bulb
electrons which flow only in one direction
direct current
electrons which oscillate back and forth
alternating current (example electric plug)
in a direct current (dc) what does the horizontal axis (x) and vertical axis (Y) represents
x=time
Y=voltage
DC is represented as a straight line since the ___ are always flowing in the same direction
electrons
ac current can be represented by what?
a sine wave
at 0, how are the electrons?
at rest
at 1, electrons have reached max flow, the voltage is at its___
highest point
at 2, electrons go to zero voltage again momentarily and ____ directions
shift
at 3, the electrons have reached _____potential in the opposite direction
maximum
how often does the oscillation happen with AC
1/60 of a second. every 1/60 of a second it changes direction. 60 cycles every second
AC is how many Hz current?
60Hz
how is electric power measured?
in Watts (W)
our common household items operate between 500-1500W, the x ray imaging system requires how much?
20,000-150,000 (W)
one watt is equal to what?
1 amp flowing through an electric potential of volt
around 1000 BC, shepherds and dairy farmers in Magnesia would use a ____to find water
lodestone
when suspended from a string the lodestone would rotate back and forth when it came to rest it would point towards ____
water
what was the lodestone really pointing too?
magnetic north
any charged particle in motion creates……
a magnetic field
can you sense magnetism?
no, it is difficult to detect and measure
the magnetic field of a charged particle in motion is ….
perpendicular to the motion of that particle
the magnetic field is neutralized how?
in magnetic pairs
atoms with an odd number of electrons in any shell have a very small…
electric field
spinning electric charges induce a magnetic field along the ……of the spin
axis
lines of a magnetic field do not start or end such as with an electric field. this continuous field is called ______
bipolar or dipolar
current that flows in an infinitesimally(minute) small loop
magnetic dipole
an accumulation of many atomic magnets with their dipoles aligned
magnetic domain
how are magnetic domains distributed normally?
randomly
when exposed to an external magnetic field, the domains can ____
align
if all the magnetic _____ in an object are aligned, it acts like a ___
domains; magnet
how are magnets classified?
according to the origin of the magnetic property
natural magnets
the earth, lodestones
artificially induced permanent magnets
iron bar magnets, compass
wire wrapped around an iron core
electromagnets
a magnetic field is created when….
a current is conducted through the electric wire
the intensity of the magnetic field is ________to the current
proportional
the higher the current, the greater the ____ of the magnetic field
intensity
materials which are weakly repelled by either magnetic pole
diamagnetic
materials which are strongly attracted by a magnet and can be permanently magnetized
ferromagnetic
types of ferromagnets
iron,cobalt and nickel
these materials are slightly attracted to a magnet
paramagnetic
material which are unaffected by a magnetic field, wood, glass
nonmagnetic
the imaginary lines of a magnetic field leave the north pole and ____return to the ___pole
leave; south
the SI unit for magnetic field strength
tesla (T)
magnets on our fridge are about how many teslas?
100mT
an MRI operates at how many teslas?
3T
what was a precursor to the modern battery?
a voltaic pile
Italian physicist in the 1700s that used zinc and copper plates to create an electric current
Alessandro Volta
who discovered a link between electric and magnetic forces?
Hans Oersted in 1820
an electric current is induced in a circuit if some part of that circuit is in a changing magnetic field
electromagnetic induction
Faraday’s Laws( 4 of them)
the magnitude of the induced current depends on four factors:
- the strength of the magnetic field
- the velocity of the magnetic field as it moves past the conductor
- the angle of the magnetic field to the conductor
- the number of turns in the conductor
2 basic parts of an induction motor
stators and a rotor
what are stators?
stationary electromagnets
The smallest unit of electrical charge is the _____.
electron.
Like charges _____ and unlike charges _____.
Like charges repel and unlike charges attract.
Electrostatic force is _____ proportional to the distance between charges, and _____ proportional to the product of the charges.
Electrostatic force is inversely proportional to the distance between charges, and directly proportional to the product of the charges.
On the surface of an electrified object, the charges concentrate on the _____.
sharpest curvature.
A _____ is a source of direct current.
battery
What is the unit of electric potential?
volt
An electric potential applied to a conductor produces _____.
When an electric potential is applied to a conductor, both an electric current and a magnetic field are produced.
An alternating (AC) current is represented by a _____ line.
sinusoidal line
A _____ uses direct current.
A flashlight is battery operated, and batteries use direct current.
Alternating current is produced by a _____.
generator.
What is Ohm’s law?
Ohm’s law is I = V/R
A charged particle in motion creates a(n) _____.
magnetic field.
Electrical power is measured in _____.
watts.
Rubber and glass are _____.
insulators because they are nonconductors.
When a group of dipoles are aligned, they create _____.
a magnetic domain
In the United States, alternating current goes through a complete cycle every _____ second.
1/60 second.
What is the SI unit of magnetic field strength?
tesla or gauss.
The force between magnetic poles is proportional to the _____ of the magnetic pole strengths, divided by the _____ of the distance between them.
The force between magnetic poles is proportional to the PRODUCT of the magnetic pole strengths, divided by the SQUARE of the distance between them.
What type of material can be made magnetic when placed in an external magnetic field?
Ferromagnetic material
Like magnetic poles _____ and unlike magnetic poles _____.
Like magnetic poles REPEL and unlike magnetic poles ATTRACT.
Water is a _____ material
diamagnetic
The magnetic intensity of an electromagnet is greatly increased by the addition of a(n) _____ core
iron
A magnetic field is produced by
electric charges in motion
A generator is a device that converts
mechanical energy to electrical energy.
A motor is a device that converts
electrical energy into mechanical energy.
A transformer with more secondary windings than primary windings
has a greater secondary voltage
The turns ratio of a transformer is determined by the
number of windings
All of the following are true of induction motors EXCEPT:
- They use multiphase current and can turn at varying rpm.
- Motor power can be regulated by the characteristics of the electromagnets that make up the stator.
- Their design is inherently weak with regard to power.
- They are used to spin the x-ray tube anode disk.
3.Their design is inherently weak with regard to power.
The electric field of a positive electric charge points____________, the electric field of a negative electric charge points___________
OUTWARD;INWARD
Increasing the product of electric charges will ___________electrostatic force
increase
Increasing the distance between electric charges will_____________elestrostatic force.
decrease
Electric current is always ___________ electron flow.
opposite
Electricity flows easily through ___________, but does not flow through_________.
copper or wood; a conductor or an insulator
What material behaves sometimes as a conductor and sometimes as an insulator?
semiconductor
What type pf material is greatlly influenced by temperature?
superconductors
One ampere is equal to:
1 Coulomb per second
Which of the following is NOT a variation of Ohm’s Law?
1. V=IR
- R=V/I
- V=IRR
- I=V/R
V=IRR
A series circuit contains 3 resistors of 5 Ohms, 10 Ohms and 15 Ohms. what is the toal resistance of the circuit?
30 ohms
What type of current is wired to our homes and businesses?
AC
What type of current must an X ray imaging system use
DC
Which of the following is not a variation of the formula for electric power?
- V=IR
- P=IV
- P=IIR
- P=I2R
V=IR
Magnetic field lines are ____________to the plane of travel of a charge.
perpendicular
Adding loops to a solenoid will
Increase the intensity of the magnetic field
Magnetically, an electromagnet acts ________________ as a bar magnet.
the same
In an electromagnet, current effects the magnetic field:
Directly
In an induction motor, _______________is responsible for causing the rotation of the rotor.
stators and electromagnets
The current of a series circuit is measured in three places with results of 10A, 10A and 10A. What is the total current of the circuit?
10A
The voltage of a series circuit is measured in 3 different places with results of 10V, 10V and 10V. What is the total voltage of the circuit?
30V
The current of a parallel circuit is measured in three places with results of 10A, 10A and 10A. What is the total current of the circuit?
30A
The voltage of a parallel circuit is measured in 3 different places with results of 10V, 10V and 10V. What is the total voltage of the circuit?
10V
If a transformer has 10 turns on the primary coil and 100 turns on the secondary coil, what is the turns ratio?
10:1
A transformer has 1000 turns in the primary coil and 10 turns in the secondary coil. It is supplied with 50 a and 1000 V, what is the output current and voltage?
10 volts secondary and 5,000a
A parallel circuit contains 3 resistors that are each 10 Ohms. What is the total resistance of the circuit?
.1+.1+.1=.3 reciprocal of .3 is 3.33<—–answer
