If the potential difference applied to the tube is doubled and the separation between the filament and the target is also doubled, the cutoff wavelength

The cut-off wavelength is given by:


where, λmin is the cut-off wavelength, h is the Planck’s constant (6.62607004 × 10-34 m2 kg / s), c is the speed of light in vacuum, e is the charge of the electron and V is the potential difference applied at the ends of the tube
So, doubling the applied potential will reduce the cut-off wavelength by half.

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