Another question on который, how is it used here?

Question

Он уже даже хотел начать изучать физику, которую в шутку называл физикой-мизикой...

I'm having trouble identifying how the subordinate clause links to the main clause, specifically, how the antecedent works. is it

1. ... physics, which is called 'something'

or

2. calling physics 'something'

To illustrate my confusion, in English you can say:

1. The book which i am reading.

the sentence can be broken into "The book" and "I am reading the book."

2. The book which is interesting

which one does the который in the example work like?

Answer 1

The option 2 calling physics 'something' is correct

A synonymous sentence would look like

Он уже даже хотел начать изучать физику, в шутку называя её физикой-мизикой -
He even was about to start learning physics facetiously calling it physics-shmysics

But the literally accurate translation of the original was provided by Alex_ander in the comment

The female pronoun in Accusative которУю refers to female noun in Accusative физикУ.

Answer 2

Он уже даже хотел начать изучать физику, которую в шутку называл физикой-мизикой...= которую (он) называл (which he called ).=он называл физику...= he called physics something

1 physics, which is called 'something'=физику, которая называлась(passive) or

2 calling physics 'something'= называя физику чем-то(participle-gerund)

Considering all the examples you can choose the equivalent.