Radiographic Science What is energy? z You can’t see it You can’t hold it Fundamental to life z Conservation of energy: z z Energy Conversions – Forms of energy z “Energy cannot be created or destroyed, only converted from one form to another” Electromagnetic energy What forms of energy are there? – – Chemical Energy Mechanical Energy z z z – – – – – Potential Energy (Compressed spring) Gravitational Energy (Pencil held above the floor) Kinetic Energy (Moving car) Sound energy Electrical energy Thermal energy Nuclear energy Electromagnetic energy 1 Energy conversions z Experiment: – Pick a pencil / pen up and then drop it on to the floor – What happens? Energy conversions z What energy conversions happen in the following video clip? Potential energy --- Kinetic energy ---- Sound energy --- Thermal energy Energy conversions z The X-ray tube is another example where energy is converted from one form (i.e. electrical) in to other forms (X-rays, heat & light) Energy conversions z What are the energy conversions taking place? Chemical energy Kinetic Sound Thermal Potential energy into sound 2 Energy conversions z What are the energy conversions taking place? Energy conversions z Chemical energy Thermal, light & electromagnetic energy Kinetic energy How do we measure energy? z z The unit of measurement for energy is the Joule (J) Have a look at the back of food packets – – z z What energy conversions are taking place? Chemical energy Kinetic Gravitational Sound Thermal Heat z What is heat? – – Energy is normally stated in Kilo Joules i.e. 484 kJ The energy may also be stated in Calories 1 Joule is equal to stretching a 10 cm rubber band to 3 times its normal length – A form of energy When applied to an object, it’s atoms vibrate more quickly: They have more kinetic energy and the object gets hotter Absolute zero (-273°C) atoms stop vibrating 3 The Transfer of heat z z The environment in which an object is situated will determine it’s temperature A hot object will transfer heat to its cooler surroundings, until the temperature is the same Thermal conduction z The transfer of heat energy due to a transfer of kinetic energy by collisions between the atoms in physical contact with each other z The rate of conduction increases with the area of the object, the ability of the material to conduct heat and the temperature difference in the room / environment z Heat conduction decreases with the length / thickness of the object (important) Heat transfer methods z z z Thermal Conduction Thermal Convection Thermal Radiation Why is this important? 4 Thermal conduction z z Thermal convection Metals are the best conductors of thermal energy Non-metals (plastic / wood) are the worst conductors of thermal energy. z z The transfer of heat in a liquid or gas As kinetic energy is transferred to the molecules: – – z z Molybdenum has a relatively low thermal conductivity Copper has a much higher thermal conductivity – – z – Find out where these materials are used in radiography and why! Thermal radiation z z z they expand become less dense Rise Carry the thermal energy with them Convection cannot occur in a vacuum Heat - Summary The transfer of heat energy by infrared electromagnetic waves This is how the energy (heat) from the sun reaches us All objects at a temperature above absolute zero radiate heat to their cooler surroundings. z z The amount of heat radiated from a hot object is more efficient at higher temperatures. This principle is very important in the removal of heat from an X-ray tube. Thermal image of a cat 5 Example MCQ’s z z z z z z Q1-Forms of energy do NOT include a electricity b magnetism c sound d kinetic e chemical Example MCQ’s z z z z z z The units of energy measurement are a coulombs b watts c joules e Celsius f sieverts Example MCQ’s Example MCQ’s Thermal conduction is z a The transfer of heat energy in a liquid z b The transfer of heat energy by infrared electromagnetic waves z c The transfer of heat in a gas z d The transfer of heat energy due to a transfer of kinetic energy z f The transfer of heat energy by infrared electromagnetic waves The electromagnetic spectrum does NOT include z a gamma radiation z b X-rays z c Radio waves z d ultraviolet rays z e Beta particles 6 Example MCQ’s The total amount of energy in a closed system is... z a variable z b constant z c Measured in watts z d always less than 1 Joule z e always more than 1 Joule 7