Understanding the Basics
* Momentum of a Photon: Photons, though massless, carry momentum. This momentum is related to their energy and wavelength by the equation:
* p = h/λ (where p is momentum, h is Planck's constant, and λ is wavelength)
* Reflection: When a photon reflects off a surface, its direction of travel reverses.
Change in Momentum
1. Initial Momentum: Let's say the photon is initially moving to the right with momentum *p*.
2. Final Momentum: After reflection, the photon is moving to the left, so its momentum is now *-p*.
3. Change in Momentum: The change in momentum is the final momentum minus the initial momentum:
* Δp = (-p) - p = -2p
Therefore, the change in momentum of a photon reflected from a mirror is twice the initial momentum of the photon, and its direction is reversed.
Key Point: The mirror itself experiences an equal and opposite change in momentum, conserving the total momentum of the system. This is a fundamental principle of physics known as the conservation of momentum.
