8. find the momentum of a photon in ev/c and in kg. m/s if the wavelength is (a) 400nm ; (b) 1 å = 0.1 nm, (c) 3 cm ; and (d) 2 nm .

We use the formula: p = E/c where E = hc / λ. hence, p = h/  λ. where h is the Planck's constant: 6.62607004 × 10-34 m2 kg / s and λ is the wavelenght. 

a) p = 6.62607004 × 10-34 m2 kg / s / 0.1 x10^-9 m = 6.62607 x 10-24 m kg/s
b) p = 6.62607004 × 10-34 m2 kg / s / 3 x10^-2 m = 2.20869 x 10-32 m kg/s
b) p = 6.62607004 × 10-34 m2 kg / s / 2 x10^-9 m = 3.3130 x 10-25 m kg/s