What do we mean when we say that energy levels are quantized in atoms? under what circumstances can energy level transitions occur?

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?

If a simple machine reduces the strength of a force, what must be increased?

Which compound is held together by the electrostatic force between two ions? a. co2 b. cci4 c. h2s d. mgf2