# Interference of light (perpendicular plains)

## Main Question or Discussion Point

Hi,

Apologies if this is a really basic question, but I'm not a physicist by training. I was wondering how two waves of plane-polarised light will interfere if they have equal intensity, are completely in phase, but their planes of oscillation are perpendicular to one another?

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sophiecentaur
Gold Member
Hello and welcome to PF. Not a bad question, at all, actually.
There will be a resultant of the addition of the two waves. The E field vectors will add together, according to the phases of each and the resultant, at any point, will be a new vector, in a different plane from the two planes you started with. According to the phases and amplitudes of the two sources, the resultant may have plane polarisation (in phase addition) or elliptical polarisation (sorry- a new idea, perhaps- but it's what you get when the two are not in phase).
It's hard to recommend a suitable link for you, as I don't know your level of knowledge but this link could be interesting as it has some good diagrams in it.
Many VHF f.m. sound transmissions (in the UK, at least) use circular or mixed polarisation and it is often achieved using a mixture of VP and HP transmitting aerials - which is just what your question is about, am.

Hello and welcome to PF. Not a bad question, at all, actually.
There will be a resultant of the addition of the two waves. The E field vectors will add together, according to the phases of each and the resultant, at any point, will be a new vector, in a different plane from the two planes you started with. According to the phases and amplitudes of the two sources, the resultant may have plane polarisation (in phase addition) or elliptical polarisation (sorry- a new idea, perhaps- but it's what you get when the two are not in phase).
It's hard to recommend a suitable link for you, as I don't know your level of knowledge but this link could be interesting as it has some good diagrams in it.
Many VHF f.m. sound transmissions (in the UK, at least) use circular or mixed polarisation and it is often achieved using a mixture of VP and HP transmitting aerials - which is just what your question is about, am.
Thanks for the reply! I'm currently looking over the slides in the link. I think I get it, but will just have to read through to make sure. One question, though: by plane polarisation, do you mean circular? Based on what I've just read in the link, won't two perpendicular light vectors with identical amplitude and phase interfere to produce circular polarlisation?

sophiecentaur