50% of the X-rays coming from a Coolidge tube is able to pass through a 0.1 mm thick aluminium foil. The potential difference between the target and the filament is increased. The thickness of aluminum foil, which will allow 50% of the X-ray to pass through, will be

Increasing the operating potential increases the penetrating power of the x-rays. Thus to allow the same fraction of x-rays to pass for increased potential, we need to thicken the foil (to aid in the attenuation process)

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