50% of the X-ray coming from a Coolidge tube is able to pass through a 0.1 mm thick aluminum foil. If the potential difference between the target and the filament is increased, the fraction of the X-ray passing through the same foil will be

More the applied potential in the Coolidge tube, more will be the energy of the x-rays and thus greater will be their penetrating power. So, more x-rays will be transmitted through the foil.

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