From the query itself, your intent is clear. It is not that you have no clarity about the other options as you are already a Post Graduate in Physics. You wanted to support the rural masses and also to pursue PhD.
My take on your query is quite different. Dreaming something is different and working on your dream to realize it is quite contrast to it. Why I am saying because the intent to help rural students is something looks like an inspiration by watching movies etc. Frankly speaking. Having done M Sc PhD, what role you would be assigned in Govt/Public Sector to promote rural people? If you want to help them, you could become a Village development Officer (VDO) and to get the post, I think any graduate is eligible for it. No need to do PG.
So, be clear. If you interested in Ph D, apply for JRF so that you can get good amount of scholarship. But remember it is so strain some to get a Doctorate and you have to struggle for a minimum period of 4 years. Of course, I presume that you are well aware of it. Having done M Sc, you are entitled to become a Lecturer in Physics in any College and you can guide those students who have the rural background at Higher secondary and Graduate level. If you want to work in Government sector, start appearing for various competitive examination from now onward. Helping the rural students would always be feasible even if you work in other capacities. As teaching appears to be your interesting subject, I suggest you to go for various options to become a Lecturer in a private/Govt. college as suggested by few experts in the preceding responses.