Physics terms ch2

What is matter?

Anything that occupies space and has mass.

What is energy?

Results when matter is altered.

What is an atom?

The fundamental unit of matter.

What determines the identity of an atom?

The composition of its nucleus and the arrangement of its orbiting electrons.

What is the nucleus?

The core of an atom.

What particles are found in the nucleus?

Protons and neutrons.

What charge does a proton have?

Positive (+).

What charge does a neutron have?

No electrical charge.

What determines an atom's atomic number?

The number of protons inside the nucleus.

What charge does an electron have?

Negative (-).

Where do electrons travel?

Around the nucleus in well-defined paths called orbits or shells.

What keeps electrons in their orbits?

Electrostatic attraction, also called binding energy or binding force.

Where is binding energy the greatest?

In the shell closest to the nucleus.

What is an ion?

An atom that gains or loses an electron and becomes electrically unbalanced.

What is ionization?

The process of converting an atom into ions.

How can x-ray photons cause ionization?

They interact with the materials they penetrate and can cause atoms to gain or lose electrons.

What is radiation?

The emission and propagation of energy through space or a substance in the form of waves or particles.

What is radioactivity?

The process in which certain unstable atoms or elements spontaneously disintegrate while trying to attain a more balanced nuclear state.

When is a substance considered radioactive?

When it gives off energy as particles or rays because of disintegration of atomic nuclei.

Are radiation and radioactivity the same thing?

No. Radiation ≠ radioactivity.

What type of radiation is used in dentistry?

X-radiation.

What is ionizing radiation?

Radiation capable of producing ions.

What are the two classifications of ionizing radiation?

Particulate radiation and electromagnetic radiation.

What is particulate radiation?

Tiny particles traveling in a straight line at high speeds.

How does particulate radiation transmit kinetic energy?

Through extremely fast-moving small masses.

What is electromagnetic radiation?

The propagation of wavelike energy without mass through space or matter, creating electric and magnetic energy.

Is all electromagnetic radiation ionizing?

No. Some electromagnetic radiation is non-ionizing and has low energy.

What are photons?

Bundles or clusters of energy that travel through space carrying electromagnetic radiation.

Do photons have mass or weight?

No.

How fast do photons travel?

At the speed of light.

Do photons ever rest?

No. They travel at the speed of light and never rest.

What two concepts describe how electromagnetic radiation moves?

The particle concept and wave concept.

What are the three characteristics of waves?

Velocity, wavelength, and frequency.

What is velocity?

The speed of a wave.

What is wavelength?

The distance between the crest of one wave and the crest of the next.

What is frequency?

The number of wavelengths or cycles that pass a certain point in a given amount of time.

What is the relationship between wavelength and frequency?

They have an inverse relationship.

What happens to frequency when wavelength increases?

Frequency decreases.

What happens to frequency when wavelength decreases?

Frequency increases.

What type of wavelength does low-frequency radiation have?

A long wavelength.

How much energy does low-frequency radiation have?

Low energy.

What type of wavelength does high-frequency radiation have?

A short wavelength.

How much energy does high-frequency radiation have?

High energy.

What determines the amount of energy in electromagnetic radiation?

Wavelength and frequency.

What determines an x-ray's ability to penetrate an object?

Its wavelength and frequency.

What is x-radiation?

A high-energy, short-wavelength, high-frequency ionizing electromagnetic radiation that can penetrate matter.

Can x-rays penetrate solids?

Yes.

What two concepts describe the movement of x-rays through space?

Particle and wave concepts.

What happens first when a dental x-ray machine is turned on?

Electricity flows through the machine.

What happens to electrons before the exposure button is pushed?

They are collected at one end of the tubehead.

What happens when the exposure button is pushed?

Electrons are propelled toward the other end of the tubehead.

What material do electrons interact with to create x-rays?

Tungsten.

How do x-rays leave the tubehead?

Through an opening in the metal housing.

What is the purpose of the metal housing of the tubehead?

It contains the x-ray tube and transformers and prevents x-rays from escaping.

What is the purpose of insulating oil?

It surrounds the x-ray tube and prevents overheating.

Where are x-rays made?

In the x-ray tube.

What is the purpose of the tubehead seal?

It seals the oil and provides an area where x-rays are allowed to exit the tubehead.

What is the purpose of transformers?

They alter, increase, or decrease voltage.

What is the purpose of the aluminum disks?

They filter out nonpenetrating, longer-wavelength x-rays.

What is the purpose of the lead collimator?

It restricts the size of the x-ray beam.

What is the purpose of the position-indicating device (PID)?

It aims and shapes the x-ray beam.

What does the glass vacuum x-ray tube contain?

Leaded glass housing, an unleaded window, a cathode, and an anode.

What is the purpose of the leaded glass housing of the x-ray tube?

It prevents x-rays from escaping.

What is the purpose of the unleaded glass window?

It permits the x-ray beam to exit and directs the beam toward the PID.

What is the cathode?

The negative electrode that supplies the electrons necessary to generate x-rays.

What is the anode?

The positive electrode that converts electrons into x-ray photons.

What charge does the cathode have?

Negative (-).

What charge does the anode have?

Positive (+).

What does the tungsten wire filament do?

It produces electrons when heated.

What does the molybdenum cup do?

It focuses electrons into a narrow beam.

What does the number of electrons equal?

Amperage.

What unit measures electron current inside the tubehead?

Milliamperes (mA).

What does mA control or represent?

The number of electrons/electron current.

What is the tungsten target?

The focal spot on the anode that converts electrons into photons.

What does the copper stem do?

It dissipates heat from the tungsten target.

What is voltage?

The force required to propel electrons from the cathode to the anode.

What unit is used to measure voltage in the x-ray tube?

Kilovolts (kV).

How many electrical circuits are within the tubehead?

Two.

What are the two electrical circuits within the tubehead?

The low-voltage (filament) circuit and the high-voltage circuit.

What does the low-voltage or filament circuit control?

The current at the filament.

What setting controls the low-voltage circuit?

mA.

What does the high-voltage circuit do?

Provides the power required to propel electrons to the tungsten target and create x-rays.

What setting controls the high-voltage circuit?

kV.

What is a transformer?

A device used to increase or decrease voltage in an electrical circuit.

How many transformers are used to adjust the electrical circuits?

Three.

What are the three transformers used in the x-ray machine?

Step-down transformer, step-up transformer, and autotransformer.

What does the step-down transformer do?

Decreases incoming 110- or 220-line voltage to the 3–5 volts used by the filament circuit.

Why does the filament circuit need 3–5 volts?

To heat the tungsten filament and create electrons.

What does the step-up transformer do?

Increases incoming wall voltage to 65,000–100,000 volts for the high-voltage circuit to make x-rays.

What does the autotransformer do?

Corrects for minor fluctuations in current.

Where does the initial electricity used to generate x-rays come from?

The wall outlet.

Where is current first directed during x-ray production?

To the filament circuit.

Which transformer controls the filament circuit?

The step-down transformer.

How many volts does the filament circuit use?

3–5 volts.

What does the filament circuit heat?

The tungsten filament in the cathode.

What is thermionic emission?

The release of electrons when the tungsten filament is heated.

What happens to electrons immediately after thermionic emission?

They have low energy and form a cloud around the filament.

What circuit is activated when the exposure button is pushed?

The high-voltage circuit.

What voltage enters the step-up transformer?

110–220 volts.

What voltage does the step-up transformer produce?

65,000–100,000 volts.