Energy of a photon:
The energy of a photon is given by the equation E = hf, where E is the energy, h is Planck's constant (6.626 x 10^-34 J.s), and f is the frequency of the photon.

Converting energy to joules:
To convert the energy of the photon from electron volts (eV) to joules (J), we use the conversion factor 1 eV = 1.6 x 10^-19 J. Therefore, the energy of the photon is 3.0 eV * (1.6 x 10^-19 J/eV) = 4.8 x 10^-19 J.

Calculating the momentum:
The momentum of a photon is given by the equation p = E/c, where p is the momentum, E is the energy, and c is the speed of light (3 x 10^8 m/s).

To find the momentum of the photon, we divide the energy by the speed of light: p = 4.8 x 10^-19 J / (3 x 10^8 m/s) = 1.6 x 10^-27 kg.m/s.

Therefore, the momentum of the photon with an energy of 3.0 eV is 1.6 x 10^-27 kg.m/s.