An LED is useful because when a current passes through it, it gives out... what? Enter your answer

In what direction does the medium move relative to the direction of the wave? explain.

Could someone . i have tried to solve myself but my calculation is off

Which are advantages of renewable resources? check all that apply. renewable energy supplies are completely reliable everywhere. some renewable resources will never be used up. little or no waste is produced by renewable resource plants. electricity can be generated in large quantities. many renewable energy facilities have lower operating costs.