Chapter 4 - Basic Physics for Radiography Flashcards
What is matter?
Matter is defined as anything that occupies space and has shape or form. The three basic forms of matter are solids, liquids, and gases. The quantity of matter that makes up any physical object is called its mass.
Laws of Conservation
Matter can be neither created nor destroyed, but it can change form.
Energy can be neither created nor destroyed, but it can change form.
Atoms
The fundamental particles that compose atoms are neutrons, protons, and electrons.
Electron Shells
Shell Number Shell Symbol Maximum Number of Electrons
1 K 2
2 L 8
3 M 18
4 N 32
5 O 50
6 P 72
7 Q 98
ionization
This process, which is called ionization, produces an atom with an electric charge.
Energy
Energy is defined as the ability to do work. It occurs in several forms and can be changed from one form to another. Some familiar forms of energy include heat, light, and electricity. Scientists have categorized energy in various ways. One method classifies energy into the following types: mechanical, chemical, thermal, nuclear, electric, and electromagnetic.
Mechanical energy
Mechanical energy can be further classified as either kinetic energy or potential energy. Kinetic energy is energy of motion, the ability of a moving object to do work. For example, a bowling ball in motion has energy to knock down the pins. Potential energy can be thought of as “stored” energy. When a bowling ball has been lifted, the work required to raise it is “stored” in the ball because of its position. When the ball is released, its potential energy is also released and is converted into kinetic energy.
Chemical energy
Chemical energy is released through chemical changes in atoms or molecules. An example of chemical energy is fire.
Thermal energy
Thermal energy is commonly called heat and is the result of atomic motion. As temperature rises, electrons move faster in their orbits and the orbits expand, which causes the electrons to move farther from the nucleus. This phenomenon explains why matter expands in size when heated and contracts when cooled.
Nuclear energy
Nuclear energy is the energy released by radionuclides. This is the energy used to produce electricity in a nuclear power plant or the explosion of a nuclear bomb.
Electric energy
Electric energy, or electricity, is the ability of electric charges to do work.
Electromagnetic energy
Electromagnetic energy is the important energy we deal with every day in radiology. This energy consists of light, x-rays, radio waves, microwaves, and other forms of energy. These energies have both electric and magnetic properties, changing the field through which they pass both electrically and magnetically (Fig. 4.5). These changes in the field occur in the form of a repeating wave, a pattern that scientists call a sinusoidal form or sine wave (Fig. 4.6).
wavelength
More important in radiology is the distance from one crest to the next, or wavelength (Fig. 4.8).
frequency
The frequency of the wave is the number of times per second that a crest passes a given point (Fig. 4.9).
velocity (speed)
Electromagnetic energy moves through space at the velocity (speed) of approximately 186,000 miles/s. All electromagnetic energy moves at the same velocity.
