Physics

That branch of science that deals withmatter and energy and their relationshipto each other.

Examples:MagnetismElectricityElectromagnetism

Equivalencies – English, Metric, Scientific Notation

Some Relationships You Must Know:

Fundamental Units of Measure

Consist of measurements relating tolength, mass and time.

Length:Fundamental unit – Meter (approx. 3 ft)

100 cm in meter = .01 meter, 10-2, 1/100

1 inch = 2.54 cm

Conversion from English to metric system(# Total inches X 2.54) – 4 inches X 2.54 = 10.16 c.m.

Conversion from metric to English system(# Total c.m. / 2.54) 10.16 c.m./ 2.54 = 4 inches(40 inch SID X 2.54 = 101.6 c.m.)

In radiology, the angstrom is often used to measure wavelength of x-rays and light.1 A = 1 X 10-10 meters

Fundamental Units of Measure

Mass – The quantity of matter in a body(inertia) • Determined by weighing• unit of mass = kilogram• 1 kg = 2.2 lb

• conversion from English to metric ( # total lbs/ 2.2), 120 lbs/ 2.2 = 54.54 kg

• conversion from metric to English (# total kg X 2.2), 54.54 kg X 2.2 = 119.988 lb

Fundamental Units of Measure

Time• unit of measure is seconds• milliseconds are used often in radiology• milli = 1/1000 sec., .001 s, 10 -3

• To convert milliseconds to seconds, move the decimal point 3 places to the left.• To convert seconds to milliseconds, move the decimal point 3 places to the right

Other Commonly Used Units of Measurement inRadiology

Amps – # of electrons flowing per second• Often expressed in milliamps• 300 mA = .3 A

ExposureREM – Measures biologic effect of radiation• Often given in millirem (mrem) 50 mrem = .05 remRAD – Measures absorbed doseRoentgen – Ionization in air

Voltage – Energy (push) behind electrons• Usually given in kilovoltage (kVP)• 100 kVp = 100,000 volts

Know what each of the above units measure

Energy

The ability to do work

Potential Energy – The ability to do workby virtue of position

Kinetic Energy – Energy in motion

Law of Conservation of Energy

Energy can neither be created nor destroyed

• If may change forms, but will not cease to exist

• Examples: - Production of x-ray results in changing electron’s energy to x-ray and heat

- Interaction between x-ray and body matter results in transferring original energy of radiation to electrons or nucleus of atoms