How long is copyright law applicable on a book? Or after how many years does copyright expire?

Answer 1

Its sixty years in India, the Copyright Act, 1957,section 22 provides Term of copyright in published literary, dramatic, musical and artistic works - Except as otherwise hereinafter provided, copyright shall subsist in any literary, dramatic, musical or artistic work (other than a photograph) published within the lifetime of the author until [(Note: Subs. by Act No.13 of 1992, S.2, w.e.f. 28-12-1991. In this regard S.3 of Act No.13 of 1992 reads: "3. Copyright not to subsist if term has expired - For the removal of doubts, it is hereby declared that copyright shall not subsist by virtue of this Act in any work in which copyright did not subsist immediately before the commencement of this Act.") sixty years] from the beginning of the calendar year next following year in which the author dies.
Explanation – In this section the reference to the author shall, in the case of a wok of joint authorship, be construed as a reference to the author who dies last.

Answer 2

Life of the author + 70 years unless published before 1923, in which case it is expired.

Answer 3

It is always best to go straight to the source:

http://www.copyright.gov/help/faq/faq-duration.html

According to the Copyright office, it depends on the work and when it was published.

Answer 4

25 years.