Radiographic Science What is energy? Forms of energy Electromagnetic energy

Radiographic Science
What is energy?
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You can’t see it
You can’t hold it
Fundamental to life
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Conservation of energy:
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Energy Conversions
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Forms of energy
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“Energy cannot be created or destroyed, only
converted from one form to another”
Electromagnetic energy
What forms of energy are there?
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Chemical Energy
Mechanical Energy
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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
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Energy conversions
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Experiment:
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Pick a pencil / pen up and then drop it on to the
floor
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What happens?
Energy conversions
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What energy
conversions happen in
the following video clip?
Potential energy --- Kinetic energy ---- Sound energy --- Thermal energy
Energy conversions
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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
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What are the energy
conversions taking
place?
Chemical energy
Kinetic
Sound
Thermal
Potential energy into sound
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Energy conversions
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What are the energy
conversions taking
place?
Energy conversions
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Chemical energy
Thermal, light & electromagnetic
energy
Kinetic energy
How do we measure energy?
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The unit of measurement for energy is the
Joule (J)
Have a look at the back of food packets
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What energy
conversions are taking
place?
Chemical energy
Kinetic
Gravitational
Sound
Thermal
Heat
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What is heat?
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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
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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
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The Transfer of heat
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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
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The transfer of heat energy due to a transfer of kinetic energy
by collisions between the atoms in physical contact with each
other
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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
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Heat conduction decreases with the length / thickness of the
object (important)
Heat transfer methods
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Thermal Conduction
Thermal Convection
Thermal Radiation
Why is this important?
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Thermal conduction
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Thermal convection
Metals are the best conductors of thermal energy
Non-metals (plastic / wood) are the worst conductors
of thermal energy.
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The transfer of heat in a liquid or gas
As kinetic energy is transferred to the molecules:
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Molybdenum has a relatively low thermal
conductivity
Copper has a much higher thermal conductivity
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Find out where these materials are used in radiography and
why!
Thermal radiation
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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.
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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
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Example MCQ’s
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Q1-Forms of energy do NOT include
a electricity
b magnetism
c sound
d kinetic
e chemical
Example MCQ’s
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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
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The transfer of heat energy in a liquid
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The transfer of heat energy by infrared
electromagnetic waves
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The transfer of heat in a gas
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The transfer of heat energy due to a transfer of
kinetic energy
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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
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Example MCQ’s
The total amount of energy in a closed system
is...
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a
variable
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b
constant
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c
Measured in watts
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d
always less than 1 Joule
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e
always more than 1 Joule
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