# Study Guide for Physics Electromagnetism

All electromagnetic (EM) energy
travels at the speed of light

In the US, AC goes through a complete cycle every 1/60 of a second,
or 60 Hz and is represented by a sinusoidal (sine) wave.

Sine Wave

Frequency
the number of wavelengths that pass a point of observation per second.

Frequency is represented by
f in formula

Frequency Unit of measurement is
the hertz (Hz).

Wavelength
The distance from one point of the sine wave to the next corresponding point.

Wavelength is represented by
λ – lambda

X-ray photon energy and frequency are directly proportional,
since x-rays are part of the EM spectrum and so they travel at the speed of light.

EM spectrum interactions
EM particles interact with matter most easily when the matter is approximately the same size as the photon wavelength.

3 degrees of interactions:
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.

Magnetism:
Fundamental force with two magnetic moments.

Orbital magnetic moment:
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).

Spin magnetic moment:
as electrons themselves spin, they create a magnetic field. (This is similar motion to a planet on its axis).

Magnetic dipoles are groups of atoms with net magnetic field (both magnetic moments). also known as magnetic domains.
A magnet is created when enough of these magnetic dipoles become oriented in the same direction and/or cause them to grow in size

Magnetic lines of force (aka lines of flux or magnetic field);
these lines travel from North to South outside the magnet and from South to North inside the magnet.

The SI unit for magnetic flux is
The Weber (Wb).

The SI units for flux density (magnetic field strength) is
Tesla (T) and Gauss (G); 1 T (tesla) = 10,000 G.

Earth’s magnetic field is
comparatively very weak (1G at the poles and 0.5G at the equator).

Three classifications of magnets:
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.

Three Laws of Magnetism:
1. Repulsion-attraction
2. Inverse Square Law
3. Magnetic Poles

Repulsion-attraction
like magnetic poles repel, unlike magnetic poles attract

Inverse Square Law
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.

Magnetic Poles
Region of magnetism always exists as a dipole no matter how small it gets.

Magnetic Induction Characteristics of Materials:
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.

Permeability & Retentivity are inversely proportional to each other :
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.

Magnetic classification of materials:
Ferromagnetic
Paramagnetic
Diamagnetic
Nonmagnetic

Ferromagnetic:
Cobalt, Nickel and Iron-highly permeable; can be made magnetic when placed in an external magnetic field.

Paramagnetic:
MRI contrast-low permeability.

Diamagnetic:
Beryllium, bismuth, lead and water-weakly repelled.

Nonmagnetic:
Wood, glass & Rubber-not affected at all most due to the ionic & covalent bonds formed within the material.

Hans Oersted:
A charge in motion will create a magnetic field.

Fleming’s hand rule
demonstrate the direction of various factors, depending on situation.

Helix
a coil of wire with no current.

Solenoid
a helix with a current.

Electromagnetic
a solenoid with a ferromagnetic core; magnetic intensity is greatly increased by the addition of the iron core.

The strength of an electromagnet depends on:
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.

Electromagnets exist in the suite.
Detents and electromagnetic relays in the control panel.

Three methods to induce a current using electromagnetism:
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.

Two primary laws of Electromagnetism
2nd Law: Lenz’s Law

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.

Lenz’s Law
Induced current opposes any flux change

two types of induction
Mutual Induction and Self Induction

Mutual Induction
*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.

Self Induction
*one coil
*always present in coils with AC power
*due to inductive reactance it is useful for permitting DC while hindering AC.

A motor converts electrical energy to mechanical energy;
a generator converts mechanical energy to electrical energy.

A transformer converts electrical current
and potential energy into higher or lower intensities.

Mutual Induction-2 coils- Step Up Transformer
Voltage goes up, amperage does down.

Mutual Induction-2 coils-Step Down Transformer
Voltage does down, amperage goes up.

Autotransformer
one winding, one coil.

Four transformer core configurations
Air-two solenoids
open- two electromagnets with open ends
closed- two electromagnetic with a top and bottom
shell- two electromagnets brick; used most commonly

Shell (2 electromagnets BRICK);used most commonly
insulated
wound one on top of another
x-ray generators used these laminated

Transformer inefficiencies
I²R Loss – Copper Loss
Hysteresis – Lagging Loss
Eddy Current Loss

I²R Loss – Copper Loss
Loss of energy due to inherent resistance
* loss given off as heat
* can combat with low resistance and/or large diameter conductors.

Hysteresis – Lagging Loss
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

Eddy Current Loss
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

Wavelength and frequency are
Inversely related when dealing with EM energy.