AP EAMCET Medical 2018 Shift 1 Paper

Two parallel metal plates A and B separated by a distance 25 cm are connected to an ammeter. Photons of energy 3.28 eV are incident on the photosensitive plate A of threshold wavelength 5000 A. The minimum value of the magnetic field to be applied parallel to the plates so that the current through the ammeter becomes zero is B x 10−5 T. Then the value of B is
(mass of electron = 9 × 10−31 kg. charge of electron = 1.6 × 10−19C)