physics chapter 5 part 1

How is the study of electricity relevant to radiography?

The primary function of an x-ray imaging system is converting electricity into electromagnetic radiation

How is the study of magnetism relevant to radiography?

MRI, magnetic field safety, magnetic field laws, transformers, and induction motors

What are the properties of matter?

Has mass and occupies space, has an energy equivalence (E = mc²), and may have electric charge (electrons −, protons +)

What is electrostatics?

The science of stationary electric charges

What is electrodynamics?

The science of electric charges in motion

What is an electrified object?

An object with too few or too many electrons

What are the 3 ways electrification is created?

Contact, friction, and induction

What is actually happening during electrification?

Movement of negative electric charges (electrons)

who discovered electromagnetic induction, and when?

Michael Faraday, 1830s

What is Faraday's law (electromagnetic induction)?

A changing magnetic field induces an electric current in a circuit

What is the smallest unit of electric charge?

The electron

What unit measures electric charge, and what does 1 unit equal?

Coulomb (C); 1 C = 6.3 × 10¹⁸ electron charges

What is Electrostatic Law #1?

Unlike charges attract; like charges repel

Which direction do electric fields radiate? Do uncharged particles have one?

Outward from a positive charge and inward toward a negative charge; uncharged particles have no electric field

What is associated with each electric charge?

an electric field

What is Electrostatic Law #2 (Coulomb's law)?

Electrostatic force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them

What is the Coulomb's law formula, and what does each variable mean?

F = k(Q_A · Q_B) / d²

-F = electrostatic force (newtons)

-Q_A, Q_B = electrostatic charges (coulombs)

-d = distance between charges (m)

-k = constant of proportionality

What law does Coulomb's law follow for distance, and what is its formula?

: The inverse square law: I₁/I₂ = (d₂/d₁)²

How does electrostatic force change with distance?

Very strong when objects are close, but decreases rapidly as they separate

What is Electrostatic Law #3?

When an object becomes electrified, the electric charges are uniformly distributed throughout the object or on its surface (example: copper conductive wire)

How does wire size relate to how much electricity it can carry? Which is larger, #12 or #14 gauge?

Larger wire can carry more electricity; #12 is larger in diameter than #14 (lower gauge number = thicker wire)

What is Electrostatic Law #4?

The electric charge of a conductor is concentrated along the sharpest curvature of its surface

What are real-world applications of Electrostatic Law #4?

Personal protection devices and police "tools" (like stun guns)

What are all 4 electrostatic laws?

1-Unlike charges attract; like charges repel

2-Coulomb's law: force is very strong when objects are close and obeys the inverse square law

3-Electric charge is uniform throughout or on the surface

4- Electric charge of a conductor is concentrated along the sharpest curvature of the surface

What kind of energy do electric charges have?

Potential (stored) energy

What is the unit of electric potential, and what is it also called?

The volt (V); also called electromotive force (EMF)

What is the relationship between voltage and potential to do work?

Higher voltage = higher potential to do work

What voltage is used in US homes/offices vs. x-ray imaging systems?

110 V in homes/offices; 220 V for x-ray imaging systems and other industrial applications

What is electrodynamics, and what is it called?

The study of electric charges in motion; called current (I)

How does the direction of current compare to electron flow?

Opposite: current flows (+) to (−) (electrical engineers); electron flow is (−) to (+) (physicists)

Give two examples of the range (orders of magnitude) of voltage.

EKG: mV to µV; transmission lines: 440 kV

What is a conductor? Give examples.

Any substance through which electrons flow easily: copper wire, water (human body)

What is an insulator? Give examples.

Any material that does not allow electron flow: rubber, glass, wood, ceramic (earthlike materials)

What is a semiconductor? Give examples.

A material that acts as an insulator under some conditions and as a conductor under others: silicon (Si), germanium (Ge)

What did semiconductors lead to, and who is associated with this?

Microchips and the rise of computer technology; William Shockley (1946)

How does temperature affect resistance?

All materials resist electricity at room temperature; resistance decreases as temperature decreas

What is superconductivity?

The property of some materials to exhibit no resistance below a critical temperature (Tc); Ohm's law does not apply

When do you have an electric circuit?

When resistance is controlled and the conductor is made into a closed path

What happens to electric current when resistance increases?

Current decreases

What are the four electrical states of matter?

Superconductor, conductor, semiconductor, insulator

Superconductor: materials and characteristics?

Niobium, titanium; no resistance to electron flow, no electric potential required, must be very cold

Conductor: materials and characteristics?

Copper, aluminum; variable resistance, obeys Ohm's law, requires an electric potentia

emiconductor: materials and characteristics?

Silicon, germanium; can be conductive or resistive, basis for computer technology

Insulator: materials and characteristics?

Rubber, glass; does not permit electron flow, extremely high resistance, necessary with high voltage

battery

provides electrical potential

switch

turns circuit on and off by providing infinate resistance

transformer

increases or decreases voltage by fixed amount (ac only)

What unit measures electric charge (Q)?

Coulomb (C)

What unit measures electric current (I), and what does 1 unit equal?

Ampere (A); 1 A = 1 C flowing through a conductor per second

What unit measures electric potential?

Volt (V)

What unit measures electric power (P)?

Watt (W)

What unit measures electric resistance?

Ohm (Ω)

What is Ohm's law?

The voltage across the entire circuit or any portion of it equals the current multiplied by the resistance

What is the Ohm's law formula, its rearrangements, and what each variable means?

V = IR

R = V/I

I = V/R

V = volts

I = current (amperes)

R = resistance (ohms)

1 V across a resistance of 1 Ω produces how much current?

1 amp

If voltage doubles (resistance stays the same), what happens to current?

Current doubles

If resistance doubles (voltage stays the same), what happens to current?

Current is cut in half

What is a series circuit?

All circuit elements are connected in a line along the same conductor

Series circuit: how do you find total resistance?

Add the individual resistances: RT = R₁ + R₂ + R₃...

series circuit: what is true about current?

Current through each element is the same and equals the total circuit current

Series circuit: what is true about voltage?

The voltages across each element add up to the total circuit voltage

What is a parallel circuit?

A circuit with elements connected at their ends rather than in a line

Parallel circuit: what is true about current?

The currents through each element add up to the total circuit current

Parallel circuit: what is true about voltage?

Voltage across each element is the same and equals the total circuit voltage

Parallel circuit: how do you find total resistance?

Total resistance is inversely proportional to the sum of the reciprocals: 1/RT = 1/R₁ + 1/R₂ + 1/R₃...

In a string of lights wired in series, what happens if one bulb burns out?

The whole circuit dies; every device must function (one wire connects each bulb)

In a string of lights wired in parallel, what happens if bulbs burn out?

The others stay lit; each light has its own circuit (two wires connect each bulb)

What is current (electricity)?

The flow of electrons through a conductor

What is direct current (DC)?

Electrons flow in one direction

What is alternating current (AC)?

Electrons oscillate back and forth

In US AC power, how long is 1 sine wave, and what is the frequency?

1 sine wave = 1/60 s; 60 cycles/sec = 60 Hz

What is a watt?

: One ampere of current flowing through an electric potential of 1 volt

What is the typical power of household appliances, light bulbs, and x-ray imagers?

Household appliances: 500-1500 W; light bulbs: 30-150 W; x-ray imager: 20-150 kW

what is the electric power formula, and what does each variable mean?

A: P = IV

P = power (watts)

I = current (amperes)

V = electric potential (volts)

Why are magnetic properties hard to study?

They're difficult to detect and measure; we can't "sense" magnetic fields

How is magnetism relevant to radiography?

Magnetic fields (and the ability to create them artificially) are used to create x-rays and are fundamental to MRI

Who discovered magnets, when, and where?

Farmers in what is now Western Turkey, around 1,000 BC

What is magnetite, and what is it also called?

A naturally occurring magnet that rotates back and forth when suspended; also called lodestone

What were two early uses or beliefs about lodestone?

It allegedly pointed toward water, and it was used as a compass

Where does the word "magnet" come from?

Magnesia, the Western Turkey village where magnetite was discovered

What is spin?

The rotation of an electron, which creates a magnetic field

What is bipolar?

A magnet that has two poles

What shape are magnetic field lines?

Always closed loops

What is a magnetic dipole?

Current flowing in an infinitesimally small loop, or the small magnet created by electron spin

What is a magnetic domain?

An accumulation of many atomic magnets with their dipoles aligned

What happens if an object's magnetic domains are aligned?

The object acts like a magnet

What creates a magnetic field?

Any charged particle in motion

What are diamagnetic materials? Give examples.

Non-magnetic materials unaffected by a magnetic field: wood, glass, plastic

What are ferromagnetic materials? Give examples.

Materials strongly attracted by a magnet that can usually be permanently magnetized: iron, cobalt, nickel

What are paramagnetic materials? Give examples.

Materials between ferromagnetic and non-ferromagnetic; slightly attracted to a magnet and loosely influenced by external fields: aluminum, copper

How are magnets classified?

By the origin of their magnetic property (why the material is magnetic and where the source is)

What are the 3 classifications of magnets?

1) Naturally occurring, 2) Artificial/permanent, 3) Electromagnetic

What is a naturally occurring magnet? Give examples.

A magnet found in nature: the Earth, magnetite

What is an artificial/permanent magnet?

A magnet made by changing the material (e.g. compass); can be changed back by force or temperature change

What is an electromagnet?

Wire wrapped around an iron core; electric current causes alignment proportional to the intensity of the current

How can all matter be classified magnetically?

By the manner in which it interacts with an external magnetic field

What is magnetic susceptibility?

The degree to which various materials can be magnetized (e.g. wood in a strong field does not increase the field's strength)

What determines magnetic susceptibility?

The number of unpaired electrons in the outer shell

Magnetism is similar to what other forces?

Electrostatics and gravity

How do magnets differ from electricity regarding the smallest unit?

Electricity has a smallest unit (the electron); magnets do not, they only get physically smaller