Electromagnetics ch. 4 Flashcards
What is the primary purpose of the x-ray imaging system?
To convert electric energy ( what comes out of the wall) to electromagnetic energy (photons)
Describe the conversion that takes place from Electric energy into electromagnetic energy (EM)
- The electric is supplied to the system through the electric current
- Conversion takes place in the Tube
- Most electric energy is converted into heat
Why do x-ray rooms need to be cool in temperature?
-Because most of the electric energy is converted into heat during conversion.
When temperature in the unit becomes too high they can malfunction
Electric energy is often converted into which 4 types of energy?
- Mechanical energy
- through an electric motor - Thermal energy
ex: toaster - Chemical energy
- ex. “jumping the car” electric charge restores the chemical energy in battery - Electromagnetic energy (EM)
What is thermal energy?
Heat
____ is the study or science of stationary electric charges
Electrostatics
Define electrostatics
study or science of stationary electric charges
What are the smallest units of electricity
- Electrons
&
2.Protons
Electrons (-) travel in the ____ whereas protons are located in the ___
- Orbital shells
2. Nucleus
Most discussions concerning electric interactions involve ___ electrons
Negative
____ electrical charges refer to charges with less electrons in comparison
positive
If the atom had more electrons than protons it is considered
negatively charged
If the atom has more protons than electrons it is considered
positively charged
How is electrification created by
- contact
-In an attempt to equalize
2.Friction
-transferring of e-
3.Induction
-process of electrical fields acting on one another w/o contact
(what we use)
How does something become electrified
when it has too many or too few electrons
Of the 3 ways to create electrification, which one do we use in x-ray
Induction
-process of electrical fields acting on one another w/o contact
____ = weaker charge
___= strong negative charge
- charge
2. - Charge
Why is the earth considered a neutral ground
Because it contains infinite + & - charges and is always willing to take on more e-
aka:
- Electric ground
- Ground potential
- Zero potential
Define electrostatics
Study of stationary or resting electric charges
every particle with a charge contains an electric field that surrounds it and is directed:
____ from “positive” charges
_____ to “negative” charges
- Away
2. Inward
Describe the law of attraction
- Unlike charges attract
2.Like charges repel
= this level of attraction or repulsion= electrostatic force
Name the 4 main laws of electrostatics
- Attraction
- Coulomb’s law
- Distribution
- Concentration
Describe Columbs law
1/4 electrostatic laws
Columb= unit of charge
-The law defines the magnitude of electrostatic force
What is the relationship between electrostatic force and the product of electrostatic charges
=columb’s law
Directly proportional
& inversely proportional to a square of the distance between them
Describe Law # 3 of electrostatics
Distribution
Electric charge distribution is uniform throughout or on the surface
- Conductors: on external surfaces
- Non conductors:throughout
Describe law # 4 of electrostatics
Concentration
Electric charge of a conductor is concentrated along the sharpest curvature of the surface
What is potential energy
-What is it measured in
=stored energy
-Measured in Volts (V)
Due to the 4 electrostatic laws, all electric charges contain ______
potential energy
Define electrodynamics
Study of electric charges in motion
How do electric charges move?
modes of transportation
- Conductor
- Insulator
- Superconductor
- Semi-conductor
Describe conductors
Any substance in which electrons flow easily
EX: Copper & Aluminum, Water
Moving charges through a conductor is called?
electric current or electricity
Describe insulators
Material that does not allow for electron flow
EX:
Plastic, Rubber, Glass & Clay
Describe semiconductors
Materials that acts as both an insulator and conductor depending on conditions
Ex:
Silicon & germanium
Describe super conductors
No resistance to electron flow in cold temperatures
-Does not require potential energy
Ex: titanium & Niobium
Ohm’s law does not hold true for ____
Superconductors
In what state do all materials resist flow of electorns
Room temperature
Term for electrons moving along a wire
Electric current
-Measured in amperes (A)
Electric current is measured in ?
amperes (A)
term for an electric conductor that is made into a closed path, and resistance to the flow is controlled by varying conductor diameter / using insulators
Electric circuit
What increases resistance in a conductive wire
making wire gauge smaller or inserting circuitry elements
Increasing electric resistance =
reduced electric current
the number of electrons flowing in a circuit is the ___.
Ampere (A)
Describe resistance
-What is it measured in?
-Reduces electric current
-Measured in Ohms
Ω
____ describes the behavior of a current within the circuit ( resistance in a circuit)
Ohms law (Ω)
What is the formula for Ohms law (Ω)
V=IR
- V= potential difference in volts
- I= electric current (A)
- R= resistance
Name the elements and functions of an electric circuit
slide 39
(Study symbols)
- Resistor:
- Inhibits flow of electrons - Battery:
- Provides electric potential - Capacitor:
- Momentarily stores electric charge - Transformer: Increases or decreases voltage by fixed amount (AC) only)
What type of circuit consists of:
All circuit elements connected in a line along the same conductor
Series circuirs
Which type of circuit consists of :
Individual branches occur off of each component
Parallel circuits
Name the two types of Electric circuits
- Series circuit
2. Parallel circuit
What are the 2 types of current
AC & DC
Describe AC
Alternating current
-Electrons that oscillate back and forth
Describe DC
Direct current
-Electrons that flow in 1 direction
Electric power is measured in ?
-How many ____ does an x-ray unit require?
watts (W)
x-ray unites require 20 - 150kW
What is the formula for power
P=IV
p= power (W)
I= Amperes (A)
V=Voltage (V)
Any charged particle in motion creates a _____
Magnetic field
Term for when electrons rotate on their axis is referred to?
Electron spin
Describe the magnetic field
- Closed loops that move with charged particles
- It is perpendicular to the motion of the particle
- Lines of magnetic field do not start of end as electric field lines do
- Consists of north and south poles
small magnet created by electron orbit is known as?
Magnetic dipole
Term for when many atomic magnets with their dipoles become aligned
Magnetic domain
Name the 3 types of magnets
- Naturally occurring (earth)
- Artificially induced permanent magnet ( horseshoe/compass)
- Electromagnets
Strength of magnetic field is ____to electric current ran through the wire
proportional
Magnets are classified according to their origin of ____
Magnetic property
Why does the earth have a magnetic field
because it spins on its axis as it orbis the sun
_____ determines the ease in which a material can be magnetized
Magnetic permeability
Name the 4 types of magnetic states of matter
- Nonmagnetic
- Diamagnetic
- Paramagnetic
- Ferromagnetic
Describe non magnetic
1/4 magnetic state of matter
-Unaffected by magnetic fields
EX: wood, glass
describe Diamagnetic
-material that is weakly repelled from both poles of a magnetic field
Ex: water, plastic
Describe paramagnetic
-Weakly attracted to both poles of a magnetic field
Ex: Gadolinium
Describe Ferromagnetic
- Can be strongly magnetized
- Iron, Nickel, Cobalt
____ has high magnetic susceptibility and greatly increases the strength of the magnetic filed
Iron
Name the laws of magnetism
1. Magnetic poles (every magnet has 2 poles , N & S) 2.Repulsion/Attraction (Like poles repel & opposite poles attract) 3.Inverse square law
Ferromagnetic can made into a magnet by:
Induction
What is the unit for magnetic field strength
Tesla ( T)
A coil of wire
Solenoid
- Running a current through this creates electrons in motion which induces a magnetic field
-Magnetic field concentrated at the center of the coil
A charge in motion induces _____
a magnetic field
True or false: a charge at rest produces no magnetic field
True
____ is a current carrying coil of wire wrapped around an iron core which intensifies the induced magnetic field
Electromagnet
Law that states in order to induce a current with the use of a magnetic field , the field can not be constant , it must be changing
Faraday’s Law
Faraday determined 4 factors to define electromagnetic induction :
(VANS)
- Velocity = of magnetic field
- Angle = of conductor
- Number = of coils (turns) on conductor
- Strength = of magnetic field
What are the types of motors used in x-ray tubes
Induction motors
-rotates the anode of the tube
____ transforms electric potential and current into higher and lower intensity
(regulates current & Voltage)
Transformer
-Operates only with AC
What does “Step up” mean in the transformer
Increases volts, decrease amps
What does step down mean in transformers
Decreases volts, increases amps
What are the 3 types of transformers
1.Closed-core
2. Autotransformer
3.Shell-type
(mostly used)
What type of transformer is most currently used today
Shell type transfromer
___ is universal ground for traveling electrons
Earth
