Question

if the wavelength of a photon is doubled , then, the momentum of the photon will be

Answer 1

from d'Broglie's law, wavelength of a photon is inversely proportional to its momentum. So if the wavelength is doubled, its momentum will be halved.

Answer 2

Photons don't have a wavelength, or even energy. ... According to Quantum Theory of light proposed by Einstein, energy of a photon is equal to the product of planck's constant and frequency i.e. E=hv=hc/w (v=frequency and w=wavelength) So when wedouble the wavelength, the energy becomes half.