Electromagnetism Flashcards
Photon
smallest quantity of any time of EM radiation, atom of light
Properties of photons
Move at speed of light; travel in a sine wave
Properties of EM radiation
frequency, velocity, amplitude, wavelength
Frequency
Waves per second (Hz); =velocity/wavelength
Velocity
distance in time (m/s); =frequency*wavelength
Amplitude
intensity of the wave
Wavelength
A=velocity/frequency
Electromagnetic Wave equation
C = frequency*wavelength (frequency and wavelength are inversely proportional)
Inverse Square Law
I1/I2 = (d2/d1)^2
Wave-Particle Duality
Electromagnetic radiation has properties of both a wave and a particle (travel through space as a wave and have ability to ionize)
Electromagnetic Spectrum
Gamma Rays (highest energy, highest frequency, shortest wavelength), UV light, Visible light, Infared, microwaves, radiofrequency (lowest energy, lowest frequency, longest wavelength)
Radiopaque
absorb x-rays; bone (absorption-high atomic number)
Radiolucent
transmit x-rays; soft tissue (transmission-low atomic number)
Attenuation
light is transmitted but scattered (translucent)
Particle Model: Quantum Theory
x-rays are identified by their energy in eV (typically 10 keV - 50 MeV
Planck’s Constant
photon energy is directly proportional to photon frequency
E=hf (h=4.15X10^-15 eVs)
Planck’s Quantum Equation
F=E/h
E=hc/wavelength
Electrostatics
branch of physics that deals with stationary or resting charges
Electrification
process by which electrons are added or ejected from matter, making the atom charged (too few or too many electrons)
Electrons
smallest unit of electron charge
methods of electrification
friction, contact, induction
Induction
electrical fields interact without touching
Conductors
copper, aluminum
Insulators
plastic, rubber, glass, wood
Semi-conductors
silicon, germanium
Law #1 electrostatic force
like charges repel, unlike charges attract
Law #2 Coulomb’s Law
electrostatic force is directly proportional to the product of the electrostatic charges and inversely proportional to the square of the distance between them
Law #3 Distribution
Electric charge distribution is uniform throughout the surface
Law #4 Concentration
concentration of charges on a curved surface is greatest where the curvature s greatest
Law #5 Movement
only negative charges can move in solid conductors
Electric potential unit
Volt
Current unit
Ampere (1 ampere = 1 coulomb/second)
Resistance unit
Ohm
Current
quantity of electrons flowing
Resistance
amount of opposition to the current in the circuit
Ohm’s Law
electric potential = current x resistance
Magnetism
materials that exert an attractive or repulsive force on other materials
Natural magnet
earth
Artificial permanent magnet
horse shoe & bar magnets made of iron
Electromagnets
wire wrapped around an iron core with electric current
Laws of magnetism
every magnet has two poles; Like charges repel, unlike charges attract; lines of magnetic field leave north pole and enter south pole
Magnetic dipole
electrons rotate around a nucleus creating a magnetic field which causes the nucleus to spin on its axis
Non-magnetized Domain
magnetic dipoles are randomly organized
Magnetized Domain
magnetic dipoles point in one direction when under influence of an external magnetic field
Magnetic Induction
non-magnetized matter placed along field line of a magnet will temporarily become magnetized and take on the properties of the magnet but will have opposite direction of field lines
Types of Magnetic Materials
Diamagnetic, ferromagnetic, paramagnetic
Diamagnetic
weakly repelled by either magnetic pole; water, plastic, copper
Ferromagnetic
strongly attracted by a magnet and can usually be permanently magnetized; iron, cobalt, nickel
paramagnetic
slightly attracted to a magnet and loosely influenced by an external magnetic field; gadolinium
Electromagnetic Phenomena
moving charged particles produce magnetic fields; a charge at rest produces no magnetic field (Oersted’s experiment)
Right Hand Rule
thumb=current
fingers=magnetic field lines
Helix
coil of wire
Solenoid
helix that has an electric current running through it and will act like a magnet by producing a north and south pole
Electromagnet
solenoid with iron core; adding iron increases intensity of magnetic field
Right hand rule for electromagnets
thumb=north pole and magnetic field lines
fingers=current
Faraday’s Experiment
Placing a magnet next to a coil didn’t produce current until the magnet was moved back and forth by the coil
3 ways to create motion between lines of force & a conductor
move the conductor
move magnetic lines of force
vary magnetic flux
Faraday’s Law
magnitude of the induced current depends on the strength of the magnetic field, velocity of magnetic field, number of turns in the conductor, angle of conductor to magnetic field
Mutual Induction
generation of an alternating current in a secondary coil by supplying an alternating current to the primary coil
Lenz’s Law
an induced current flows in the direction that opposes the magnetic field change that induces it
Self Induction
alternating current flows through a single coil of wire
Alternating current
electric current that changes direction several times a second
Electric generator
converts mechanical energy to electrical energy
Simple AC generator
single loop of wire rotated mechanically between the poles of a magent
Direct Current generator
AC generator with commutator ring which makes nondirectional current
Electric motor
generator with electric current through the wire
AC motor
as current alternates direction, magnetic field alternates polarity
DC motor
commutator ring reverses the direction in the coils
Induction motor
powers the rotating anode of an x-ray tube
Transformer
transforms electric potential to a higher or lower voltage
Step-up Transformer
voltage of secondary coil is higher than primary coil
Step-down Transformer
voltage of primary coil is higher than secondary coil
Properties of X-rays
highly penetrating; electrically neutral; invisible; form of electromagnetic radiation; wide variety of energies and wavelengths; release small amounts of heat; travel in straight lines
Oersted’s experiment
compass next to long straight wire pointed north with no current but pointed toward wire with current
Closed Core Transformer
square of ferromagnetic material; coils on opposite sides; helps reduce energy loss
Shell-type transformer
two coils around center rod; most efficient
Autotransformer
single coil around a iron core; base on self induction; not suitable for use of x-ray machines
