# If Photons do not have 'charge,' how do microwaves which use the negative and positive polarity of the wave agitate $\rm H_2O$?

As far as i have understood it, Photons do not have Charge. Charge as i have understood it is the Positive and Negative charge of an atom.

In context to $$\rm H_2O$$ being a polar molecule, microwaves ovens utilise the positive and negative polarity of the microwave to agitate the $$\rm H_2O$$ Molecules creating kinetic energy and heat.

How is it so, that an EM Wave that has no charge, is able to agitate the charged particles of $$\rm H_2O$$?

• It is simple: it is the micro-oven charges and currents that create the electromagnetic force acting on $\text{H}_\text{}2\text{O}$ Jun 15, 2021 at 10:40
• @VladimirKalitvianski That is an answer. Jun 15, 2021 at 10:55
• The microwaves are tuned to the resonant frequency of the water molecule. Jun 16, 2021 at 1:26

The charge of individual photons is indeed zero, but light, or microwaves, contain oscillating electric (and magnetic) fields. Charged particles and electrically polarized molecules such as $$\rm H_2O$$ will experience forces when they experience these electric fields.

When the microwave oven is turned on, and the microwaves pass through the water, the polar molecules of the water will constantly try to align in the appropriate direction (one that minimizes energy) with these electric fields by constantly changing their orientation inside the water (as the direction of the electric field keeps flipping).

As these molecules continually change orientation extremely quickly (millions of times per second), this vibrational motion causes the water molecules to gain kinetic energy which increases the temperature of the water.

• Would this mean that Electric Fields and Charge are fundamentally different from each other? In other words, Photons have no Charge, but they do have Electric Fields, this must mean that there is some difference here? Sorry, could you please clarify? Jun 15, 2021 at 10:48
• @Razor Photons do not have either electric or magnetic field when interacting as elementary particles. The interactions are quantum mechanical. Electric and magnetic fields belong mainly to classical, electrodynamics. It can be shown that the superposition of a large number of photons builds up a classical electromagnetic wave, but one needs to know quantum field theory well to understand the mathematics. see physics.stackexchange.com/questions/388026/… Jun 15, 2021 at 11:04
• @annav This brings great clarity. If i may ask your patience, i would like to paraphrase and see if i am roughly correct. When a large number of Photon Elementary Particles collect, they begin to collect into the standard interference pattern. Only in large numbers do photons exhibit their classic wave functions. Photons in and of themselves however do not have an electric or magnetic field. Would i be in any way correct in this paraphrasing? Jun 15, 2021 at 11:38
• @Razor It is not the "photons exhibit their classic wave functions" . Their quantum wavefunctions build up by quantum superposition the classical EM wave. The wave in "wavefunction" is a propbability wave . If you looked at the link I gave, the last frame shows the probability of the photon hitting the (x,y) of the screen. . Jun 15, 2021 at 11:52
• @annav This brings further clarity, i had a look and read through it, your patience is appreciated. Jun 15, 2021 at 12:14

Photons has zero charge, but they still can interact with electricity. They can participate in kindof "chemical" reactions with charged particles, including electrons.

Actually photon is a carrier of electromagnetism, it is "main" particle of it.

The energy of photon is $$h\nu$$, where $$\nu$$ is it's frequency. For microwaves from the oven, this formula gives very tiny value. This means, that oven's microwaves consist of a "sea" of brazillions of very tiny photons. These photons don't act individually, they act collectively. The collective action of such photons can apply some electric force on water molecule and make it rotate.

• I agree with you that only the combined influence of the countless photons in each period of the EM wave from the microwave generator can influence the molecules. See physics.stackexchange.com/questions/90646/… Jun 15, 2021 at 17:20