when a metal is heated and the electrons gain enough energy to 'boil off'
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What is an electron gun?
a heated metal wire (cathode) emits electrons which accelerate towards the positive accelerating anode, which forms an electron beam
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Why do they accelerate towards the anode?
the high voltage provides a potential difference between the cathode and anode which accelerates the electrons
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Why are electron guns put in vacuums?
to reduce interactions with other particles
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Why is the electron beam a current?
it is a flowof charged electrons
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What is current equal to?
number of particles per second x charge on each particle
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What is kinetic energy equal to?
1/2mv^2 or eV
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How is an electron beam used to form x rays?
the beam is accelerated to tens of thousands of volts then focused on a heavy metal target backed by a large metal anode (get rid of heat). when the target is positively charged the electrons collide transferring energy to x rays
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What is the inverse square law?
if the distance from the source increase, the intensity decreases by that distance squared
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What is a CAT scan?
tomography is used to produce a cross section by rotating he source/recording medium. many of these make a 3D image
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What is a fluroscope?
real time x rays by using an x ray source and a fluroscent screen made of crystals like calcium tungstate which give off light when struck by x rays
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What is an action potential?
an electrical discharge that travels through a cell membrane
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What nerve ending is stimulated in the heart?
the sino atrial nerve
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What is depolarisation and reploarisation?
depolarisation-the potential difference across the membrane becomes smaller; repolarisaition-the process reverses
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How does the heart beat?
an electrical pulse spreads through the atria depolarising them and causing a contraction, forcing blood to ventricles. the ventricles then depolarise causing a contraction, forcing blood out the heart. they both then repolarise
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What are the P, QRS and T waves on an ECG?
P=deploarisation of atria; QRS=deploarisation of ventricles; T=re-polarisation of ventricles
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What does frequency equal?
1/time period
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What are uses of an ECG?
can provide information on damaged heart muscles; heart blockages; high/low pulse rate; irregular contractions of ventricles
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What is a pacemaker?
something that regulated the heart beat by sending electrical impulses, by using electrodes in contact with the heart muscles
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What does pulse oximetery do?
determines the amount of oxygen carried by haemoglobin in the blood
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How does it take place and what situations is it good for?
1) a small sensor placed on earlobe or finger 2) a red and infrared light are sent across a sensor from different LEDs 3) a photo detector measures intesity of emerging light. useful when a patient is in surgery, recovery or intensive care
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How does this work?
the device is sensitive to oxygen bound haemoglobin and unbound haemoglobin. a measure of the percentage bound can be made based on the changing absorbances of the red and infrared light
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Other cards in this set
Card 2
Front
What is an electron gun?
Back
a heated metal wire (cathode) emits electrons which accelerate towards the positive accelerating anode, which forms an electron beam
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