Black Holes and Photons with Entropic Force

We study the entropic force effects on black holes and photons. It is found that application of an entropic analysis restricts the radial change ΔR of a black hole of radius R_H, due to a test particle of a Schwarzschild radius R_h moving towards the black hole by Δx near a black body surface, to be given by a relation R_HΔR= R_hΔx/2, or ΔR/λ_M =Δx/2λ_m. We suggest a new rule regarding entropy changes in different dimensions, ΔS= 2πkDΔl /λ, which unifies Verlinde's conjecture and the black hole entropy formula. We also propose the extension of the entropic force idea to massless particles such as photons. It is realized that there is an entropic force on a photon of energy Eγ, with F = G M (E_γ/c^2_)/R2, and therefore the photon has an effective gravitational mass m_γ= E_γ/c^2.