# Amount of energy required to change path of a photon

1. Jan 11, 2013

### San K

What is the amount of energy required to change path/trajectory of a photon by an infinitesimal amount?

In a single particle (double slit) interference, the photons land up on one of the interference fringes. (when no-which-way)

If we were to place a magnet to try to slightly change the path of the photon, (say from one of the fringes to a blob in-between)how much of the electromagnetic energy would be required? (relative to the one quanta of energy of the photon)

alternatively

are there any energy effects involved in (single particle) interference?

....the path of the photon is getting changed (after all, atleast per some of the interpretation of QM) from fringe to no-fringe co-ordinates

Last edited: Jan 11, 2013
2. Jan 11, 2013

### Staff: Mentor

3. Jan 11, 2013

### Sonderval

The amount of energy needed to change a trajectory of a particle is zero - in elastic scattering, only momentum is changed, not energy. I think in principle this should also hold for a photon.

4. Jan 11, 2013

### San K

Thanks JTbell and Sonderval.

The photon lands on a different x-coordinate when we do which-way, than when we don't.

The photon's path is being changed.

To change the path of something isn't energy (transfer) required?

5. Jan 11, 2013

### The_Duck

If you simply deflect something its energy is unchanged. Therefore no energy /can/ be transferred, by conservation of energy.