Free physics books are found on the web as frequently as birds are found in aquaria. Here are the best ones:
• For learning physics for examinations, an excellent site is Hyperphysics at hyperphysics.phy-astr.gsu.edu/hbase/hframe.html.
• The high-quality electrodynamics text by Bo Thidé, Electromagnetic Field Theory, can be found at www.plasma.uu.se/CED/Book.
• Two excellent introductory physics texts by Benjamin Crowell, Simple Nature and Light and Matter, as well as a textbook on calculus and a textbook on general relativity can be downloaded at www.lightandmatter.com.
• Pearls for every physicist are the fallacies about physical concepts collected by Friedrich Herrmann, Historical Burdens on Physics, available at www.physikdidaktik.uni-karlsruhe.de/index_en.html. Herrmann's excellent, short and freely downloadable physics textbook for secondary school, The Karlsruhe Physics Course, can also be downloaded there. This book is also recommended if you – girl or boy – need to repeat what you learned or should have learned about physics, the science of motion, before the age of 18. (If you read German, you might also read the 2013 paper by C. Strunk and K. Rincke, available here.)
• A text on quantum mechanics that uses Schwinger's approach, Quantum Principles and Particles by Walter Wilcox, as well as some other physics texts, can be downloaded at homepages.baylor.edu/open_text/.
For an extensive list of internet links to physics information see Appendix C: Sources of information on motion in the volume I of the Motion Mountain physics text.
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