A 400-line/mm diffraction grating is 3.5 cm wide. Two spectral lines whose wavelengths average to 560 nm are just barely resolved in the...

65. A 400-line/mm diffraction grating is 3.5 cm wide. Two spectral lines whose wavelengths average to 560 nm are just barely resolved in the fourth-order spectrum of this grating. What is the difference between their wavelengths? 69. What diameter optical telescope would be needed to resolve a Sun-sized star 10 light-years from Earth?