Study Guide for Physics Electromagnetism – Flashcards
Unlock all answers in this set
Unlock answersquestion
All electromagnetic (EM) energy
answer
travels at the speed of light
question
In the US, AC goes through a complete cycle every 1/60 of a second,
answer
or 60 Hz and is represented by a sinusoidal (sine) wave.
question
Frequency
answer
the number of wavelengths that pass a point of observation per second.
question
Frequency is represented by
answer
f in formula
question
Frequency Unit of measurement is
answer
the hertz (Hz).
question
Wavelength
answer
The distance from one point of the sine wave to the next corresponding point.
question
Wavelength is represented by
answer
? - lambda
question
X-ray photon energy and frequency are directly proportional,
answer
since x-rays are part of the EM spectrum and so they travel at the speed of light.
question
EM spectrum interactions
answer
EM particles interact with matter most easily when the matter is approximately the same size as the photon wavelength.
question
3 degrees of interactions:
answer
1. Transparency -Think window 2. Translucency -Think frosted glass, this is termed radiolucent or radiolucency, like lungs and some soft tissue. 3. Opacity -Think door, this is termed radiopaque or radiopacity, like Barium, bone and some soft tissues.
question
Magnetism:
answer
Fundamental force with two magnetic moments.
question
Orbital magnetic moment:
answer
as electrons orbit around the nucleus, they create a magnetic field perpendicular to their plane of orbit. (This is similar motion to a planet orbiting).
question
Spin magnetic moment:
answer
as electrons themselves spin, they create a magnetic field. (This is similar motion to a planet on its axis).
question
Magnetic dipoles are groups of atoms with net magnetic field (both magnetic moments). also known as magnetic domains.
answer
A magnet is created when enough of these magnetic dipoles become oriented in the same direction and/or cause them to grow in size
question
Magnetic lines of force (aka lines of flux or magnetic field);
answer
these lines travel from North to South outside the magnet and from South to North inside the magnet.
question
The SI unit for magnetic flux is
answer
The Weber (Wb).
question
The SI units for flux density (magnetic field strength) is
answer
Tesla (T) and Gauss (G); 1 T (tesla) = 10,000 G.
question
Earth's magnetic field is
answer
comparatively very weak (1G at the poles and 0.5G at the equator).
question
Three classifications of magnets:
answer
1. Natural-created over long period of time like loadstone, Earth. 2. Artificial Permanent-man made; can lose magnetism through heating ;/or trauma like bar or horseshoe magnet. 3. Electromagnet-Temporary; produced by moving current.
question
Three Laws of Magnetism:
answer
1. Repulsion-attraction 2. Inverse Square Law 3. Magnetic Poles
question
Repulsion-attraction
answer
like magnetic poles repel, unlike magnetic poles attract
question
Inverse Square Law
answer
the force between the magnetic fields is directly proportional to the product of their magnitudes and inversely proportional to the square of the distance between them.
question
Magnetic Poles
answer
Region of magnetism always exists as a dipole no matter how small it gets.
question
Magnetic Induction Characteristics of Materials:
answer
1. Magnetic susceptibility-the degree with which a material can be magnetized. 2. Permeability-ease with which a magnet can be magnetized. 3. Retentivity-ability of the magnet to stay magnetized.
question
Permeability ; Retentivity are inversely proportional to each other :
answer
the nail in the battery electromagnet had High permeability as it was easily magnetized, but Low retentivity as it did not keep the magnetic property.
question
Magnetic classification of materials:
answer
Ferromagnetic Paramagnetic Diamagnetic Nonmagnetic
question
Ferromagnetic:
answer
Cobalt, Nickel and Iron-highly permeable; can be made magnetic when placed in an external magnetic field.
question
Paramagnetic:
answer
MRI contrast-low permeability.
question
Diamagnetic:
answer
Beryllium, bismuth, lead and water-weakly repelled.
question
Nonmagnetic:
answer
Wood, glass ; Rubber-not affected at all most due to the ionic ; covalent bonds formed within the material.
question
Hans Oersted:
answer
A charge in motion will create a magnetic field.
question
Fleming's hand rule
answer
demonstrate the direction of various factors, depending on situation.
question
Helix
answer
a coil of wire with no current.
question
Solenoid
answer
a helix with a current.
question
Electromagnetic
answer
a solenoid with a ferromagnetic core; magnetic intensity is greatly increased by the addition of the iron core.
question
The strength of an electromagnet depends on:
answer
Diameter of the coil, length of the coil, current passing through the coil. These are all directly proportional. Increasing any of these factors, the strength of the electromagnet increases.
question
Electromagnets exist in the suite.
answer
Detents and electromagnetic relays in the control panel.
question
Three methods to induce a current using electromagnetism:
answer
1. Move an electric conductor through a stationary magnetic field. 2. Move magnetic lines of force across an electric conductor. 3. Vary the strength of a stationary magnetic field through an electric conductor.
question
Two primary laws of Electromagnetism
answer
1st Law: Farraday's Law 2nd Law: Lenz's Law
question
Farraday's Law
answer
The magnitude of the induced current depends on four factors: Strength of the magnetic field, speed of motion between the lines of force ; electric conductor, angle between the lines of flux ; conductor, number of turns in the conductor.
question
Lenz's Law
answer
Induced current opposes any flux change
question
two types of induction
answer
Mutual Induction and Self Induction
question
Mutual Induction
answer
*two coils. *Varying current to primary coil which creates a magnetic field of varying strength ? Ferromagnetic core in secondary coil in magnetized creating its own magnetic field? current is created on secondary side.
question
Self Induction
answer
*one coil *always present in coils with AC power *due to inductive reactance it is useful for permitting DC while hindering AC.
question
A motor converts electrical energy to mechanical energy;
answer
a generator converts mechanical energy to electrical energy.
question
A transformer converts electrical current
answer
and potential energy into higher or lower intensities.
question
Mutual Induction-2 coils- Step Up Transformer
answer
Voltage goes up, amperage does down.
question
Mutual Induction-2 coils-Step Down Transformer
answer
Voltage does down, amperage goes up.
question
Autotransformer
answer
one winding, one coil.
question
Four transformer core configurations
answer
Air-two solenoids open- two electromagnets with open ends closed- two electromagnetic with a top and bottom shell- two electromagnets brick; used most commonly
question
Shell (2 electromagnets BRICK);used most commonly
answer
insulated wound one on top of another x-ray generators used these laminated
question
Transformer inefficiencies
answer
I²R Loss - Copper Loss Hysteresis - Lagging Loss Eddy Current Loss
question
I²R Loss - Copper Loss
answer
Loss of energy due to inherent resistance * loss given off as heat * can combat with low resistance and/or large diameter conductors.
question
Hysteresis - Lagging Loss
answer
energy lost while magnetizing & demagnetizing the core material *loss given off as heat *coercivity-the energy that causes reorientation of the magnetic dipoles *can combat with silicon iron core
question
Eddy Current Loss
answer
current that opposes the magnetic field that produced it, causing repulsive or drag forces between the conductor and its magnet. *loss given off as heat *can combat by using a laminated layer
question
Wavelength and frequency are
answer
Inversely related when dealing with EM energy.
