what are the threshold frequencies and wavelength for electron emmission from sodium and from aluminum

Because light travels in a straight line and casts a shadow, isaac newton hypothesized that light is

Alinearly polarized electromagnetic wave has an average intensity of 196 w/m^2. this wave is directed towards two ideal polarizers (in real polarizers, transmission is also effected by reflection and absorption). polarizer a is oriented with its transmission axis at an angle of θ_1=20.8∘ with the incident electric field. polarizer b has its axis at an angle of θ_2=63.0∘ with the incident electric field. what is the average intensity of the wave after it passes through polarizer a? what is the average intensity of the wave after it passes through polarizer b? suppose that the two polarizers a and b are interchanged. what would the average intensity be after passing through both polarizers?

What would be the strength of earth's gravitational field at a point where an 80.0 kg astronaut would experience a 80% reduction in weight