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P3 Topic 2: X-rays and ECGs
X-ray machines

To produce X-rays there are four key things that are needed: a cathode, an anode, an evacuated gas tube
and thermionic emission.
1. A filament acts as the cathode, which is very hot. The heat gives energy to its electrons. When they…

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The X-rays then hit a fluorescent screen which absorbs them and fluoresces (gives off light) to show a live
image on the screen. The image we see is due to the difference in X-ray intensity ­ exposing the different
bits of the screen to different amounts of X-rays. The higher…

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The heart rate can be worked out from an ECG using: frequency (Hz) = 1/time period (seconds)


The heart has a natural pacemaker ­ a group of cells in the wall of the right atrium which produce electrical
signals that pulse about 70 times a minute.
These signals spread…


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