A sinusoidal electromagnetic wave has an average intensity of I1 =100 W/m2. By what factor would the electric-field amplitude of the wave have to be increased in order for the wave to have an average intensity of I2 = 8100 W/m2 ?

The two most prominent wavelengths in the light emitted by a hydrogen discharge lamp are 656(red) and 486 (blue). light from a hydrogen lamp illuminates a diffraction grating with 500 lines per mm, and the light is observed on a screen 1.50 behind the grating. what is the distance between the first-order red and blue fringes?