I have visited many websites in the past dedicated to providing introductory information on a variety of
physics topics but this one appears to be the most comprehensive one I have come across:

The rationale for the site is as follows: (from HyperPhysics site)

HyperPhysics is an exploration environment for concepts in physics which
employs concept maps and other linking strategies to facilitate smooth
navigation. For the most part, it is laid out in small segments or
"cards", true to its original development in HyperCard. The entire
environment is interconnected with thousands of links, reminiscent of a
neural network. The bottom bar of each card contains links to major
concept maps for divisions of physics, plus a "go back" feature to allow
you to retrace the path of an exploration. The side bar contains a link
to the extensive Index, which itself is composed of active links. That
sidebar also contains links to relevant concept maps. The rationale for
such concept maps is to provide a visual survey of conceptually
connected material, and it is hoped that they will provide some answers
to the question "where do I go from here?". Whether you need further
explanation of concepts which underly the current card content, or are
seeking applications which go beyond it, the concept map may help you
find the desired information.

There is also a CD version of the site available for a fee for  use when
internet access is not an option.