Two narrow slits spaced 0.47 mm apart are placed 77 cm from a screen. the slits are illuminated with light, and an interference pattern is observed on a screen. the distance between the first and third bright fringes is 6.8x 10^-4 m
a) what is the light's wavelength? is it visible to the human eye?
b) suppose a diffraction(multi-slit) grating is used instead of the two slits, and green(54 nm)laser shines through it onto the screen. what is the slit density of the grating?