A charged particle moving along the x-axis enters a uniform magnetic field pointing along the z-axis. Because of an electric field along the y-axis, the charge particle does not change velocity. What is the sign of this particle

When a vertical beam of light passes through a transparent medium, the rate at which its intensity i decreases is proportional to i(t), where t represents the thickness of the medium (in feet). in clear seawater, the intensity 3 feet below the surface is 25% of the initial intensity i0 of the incident beam. what is the intensity of the beam "10" feet below the surface? (give your answer in terms of i0. round any constants or coefficients to five decimal places.)